Engine Bay & Nacelle Thermal Insulation: Die-Cut Fire Barriers, Blanket Cores & Bleed-Air Duct Lagging
H-O Products die-cuts and converts high-temperature insulation materials into blanket cores, fire-barrier layers, thermal gaskets, and bleed-air duct lagging for jet-engine nacelles, firewall zones, and APU compartments — every layer cut, laminated, and kitted to your drawing. H-O is a materials converter: flight certification and zone qualification remain with the airframer and propulsion integrator.
Built for: Inlet and fan-cowl insulation blanket cores, firewall barrier layers and fire-seal gaskets, bleed-air duct lagging, APU compartment insulation, thermal break pads at hot-structure interfaces, and PTFE-coated fiberglass wear and facing layers.
To insulate an engine bay or nacelle, separate the thermal job from the fire job, then pick by zone. The two highest-volume call-outs: SOLIMIDE polyimide foam for inlet and fan-cowl blanket cores, commonly evaluated against FAR 25.856(a) flame-propagation requirements on the maker’s data, and ArmaGel HT / HTL or Pyrogel XTE aerogel blanket for bleed-air duct lagging, matched to line temperature.
Fire-barrier plies, hot-zone gaskets, fluid-exposed seals, and facing layers are mapped zone-by-zone in the When-to-spec-what list. Values are per the TDS on file; see the material reference below for ordering details.
FAR 25.853 (compartment interior flammability, cited qualitatively) · FAR 25.856(a) / (b) (thermal-acoustic insulation flame propagation and burnthrough, cited qualitatively) · ISO 2685 (resistance to fire in designated fire zones, by designation) · FAA AC 20-135 (powerplant fire protection test guidance, by designation) · AMS 3323 (fluorosilicone sponge) · ASTM C177 (thermal conductivity) · ASTM D1056 (flexible cellular materials) · UL 94 (flammability listings per TDS) · ASTM E162 / E662 (flame spread and smoke density data on silicone-foam TDS) · vendor TDS for per-grade values.
- Inlet / fan-cowl blanket core: SOLIMIDE polyimide foam
- Firewall / fire-barrier ply: ManniGlas paper or mica sheet
- Warm bleed-air duct lagging: ArmaGel HT / HTL
- Hottest duct sections: Pyrogel XTE
- Hot-zone access gaskets: BISCO HT silicone foam
- V-0 rated compartment gasket: kSil V-0 sponge
- Fuel / oil / hydraulic mist at the seal: Fluorosilicone sponge
- Radiant heat shield pad: BISCO RF-120 heat shield
- Erosion / chafe facing layer: PTFE-coated fiberglass
- APU compartment insulation: SOLIMIDE + ManniGlas stack
Where are you in the spec process?
This page serves propulsion and nacelle engineers who already hold a material call-out and engineers still mapping thermal, fire, and weight constraints. Pick the path that matches where you are; you don’t have to read the rest.
Send a drawing, get a quote
SOLIMIDE polyimide foam, ManniGlas paper, ArmaGel or Pyrogel aerogel blanket, BISCO silicone foam, kSil V-0 sponge, fluorosilicone sponge, mica sheet, or PTFE-coated fiberglass on your drawing.
Skip to the quote form →Walk through the selection factors
Six selection factors (temperature exposure, fire role, weight, vibration and erosion, fluid exposure, attachment method), a layer-stack explorer for the three classic nacelle stack-ups, and ten material families with TDS-cited test methods.
Start with selection factors →
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1Send drawingUpload a DXF, STEP, or PDF, or describe the assembly. A sample part works too.
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2Material reviewEngineering reviews the part against the vendor TDS: zone temperature and fire role, weight and thickness budget, vibration and erosion exposure, fluid contact, and how the part attaches and gets serviced.
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3PrototypeSamples typically ship in 3–5 business days for common die-cut configurations on materials we keep on hand. Made-to-order; MOQ varies by material and part.
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4ProductionStandard production runs ship about 2 weeks after drawing approval, including kiss-cut-on-liner and laminated configurations. Expedited service available. Ongoing parts run with material traceability and lot-code TDS records.
What are you insulating or protecting?
Application Zones
Five distinct material problems hide inside a propulsion installation: the nacelle inlet and fan cowl, where blanket cores must be light, stable, and shaped to the barrel; the firewall interfaces, where fire containment is the design driver and insulation is the supporting act; the bleed-air ducting, where lagging grade follows line temperature; the APU compartment, which compresses all three problems into one small bay; and the protection layers, the facings and wraps that keep airflow, chafe, and handling from destroying the stack underneath.
Click a tab to see the joint, the exposure, and the material families H-O converts for that zone.
Nacelle inlet & fan-cowl insulation cores
Inlet and fan-cowl insulation is a weight problem before it is a thermal problem. Every gram in the barrel multiplies across the fleet, which is why the working core is SOLIMIDE polyimide foam: an ultra-light, dimensionally stable foam whose flame, smoke, and toxicity behavior is documented on the maker’s data and commonly evaluated against the FAR 25.856(a) flame-propagation requirement for thermal-acoustic insulation.
[2] H-O die-cuts and profiles the foam into blanket cores, frame-bay infills, and spacer blocks that follow the barrel geometry, and laminates facings where the zone calls for them. The discipline is dimensional: cores cut to the real bay, kitted in installation order, so coverage is continuous and repeatable across ship sets. Thermal conductivity is reported per ASTM C177 on the TDS.
Firewall barriers & fire-seal interfaces
A firewall is a containment strategy, not a single material, and the converted parts in it divide cleanly: barrier plies that resist flame and radiant heat, and compliant seals that close the gaps the structure leaves. For barrier plies, the inorganic families do the work: phlogopite mica sheet for the most thermally severe locations and ManniGlas glass-fiber paper as the lighter inorganic layer in multi-ply stacks.
For the compliant seals, kSil KSV001–KSV006 sponge (UL 94 V-0, FAR 25 Appendix F, ABD0031, smoke and toxicity data, 1% compression set per TDS) and BISCO HT-series silicone foam (UL 94 V-0 / HF-1, flame-spread and smoke data per TDS) keep sealing force through vibration and thermal cycling; where the stack needs a fire-block layer behind the mica or ManniGlas ply, BISCO FPC fire-protective covering (flame-retardant silicone on reinforcing fiberglass, -55 to +200 °C, flame spread <5 per TDS) is the converted layer. Fire-zone qualification itself, the ISO 2685 / AC 20-135 test campaign, belongs to the zone designer and the test house; H-O’s role is converting the documented materials into barrier plies, gaskets, and laminated stacks that match the qualified drawing.
Bleed-air duct & hot-line lagging
Bleed-air ducting carries engine-temperature air through bays full of wiring, composites, and people during maintenance, so the lagging has two customers: the adjacent structure and the technician. Aerogel blanket changed this job; it delivers the required surface temperature in a fraction of conventional lagging thickness, which is what keeps insulated ducts inside crowded bays.
The split follows line temperature: ArmaGel HT / HTL covers warm runs as the thin flexible default, and Pyrogel XTE, rated for service to 650 °C per the maker’s data, takes the hottest sections nearest the engine.
H-O die-cuts both into fitted sleeves, saddles, flange collars, and removable wrap segments, and adds a PTFE-coated fiberglass facing where airflow erosion or repeated handling demands a hard-wearing surface. Conductivity is per ASTM C177 on each TDS; design thickness from those values for your line and bay. [8] [5]
APU compartment insulation & gasketing
The auxiliary power unit compresses every propulsion-zone problem into the tail cone: a fire-designated zone, hot exhaust-adjacent structure, dense plumbing, and an access door a mechanic opens on every turnaround.
The converted parts follow the same logic as the main bay at smaller scale: SOLIMIDE foam blanket cores against the compartment walls (HT-340, 575 °F continuous with a FAR 25.856(a) pass per TDS, on the exhaust-adjacent positions; AC grades elsewhere), ManniGlas or mica barrier plies where the fire strategy calls for them, Pyrogel XTE lagging on the exhaust-adjacent lines, and kSil KSV001–KSV006 (1% compression set, FAR 25 Appendix F data per TDS) or BISCO HT-series gaskets on the access door and equipment covers, where compression set decides whether the seal survives daily cycling.
Fluid exposure is the quiet differentiator: APU bays collect fuel and oil mist, so seals in the mist path move to fluorosilicone sponge (R10490, capable of AMS 3323 Class 2 and MIL-R-6130 Type 2 per TDS; -80 to +400 °F) rather than standard silicone. [14] [6]
Facing, wrap & wear-protection layers
Most insulation failures in service start at the surface: airflow erodes an unfaced blanket edge, a harness chafes through a facing, a boot heel crushes a core during an inspection.
The protection layer is therefore part of the insulation spec, not an accessory. PTFE-coated fiberglass is the working family: glass-cloth strength and temperature capability with a low-friction PTFE surface that sheds fluids and survives contact, supplied as facings laminated to blanket cores, slit-width wrap for lines and wire-adjacent runs, and die-cut rub strips at known chafe points.
Where the protection job is cushioning rather than surface wear, thin BISCO silicone foam plies take the local compression. H-O supplies these as flat sheet, slit roll, die-cut parts, or pre-laminated onto the insulation core, with retention methods (overlap, lacing, banding, bonded edges) defined by the system designer. [13]
Six decisions that drive your nacelle insulation spec
Propulsion-zone insulation is never a single-property choice. The right stack satisfies six independent constraints at once, and missing one produces a part that installs cleanly, passes inspection, and degrades in service when the zone runs hotter than the nominal limit, a fluid finds the wrong elastomer, or vibration grinds an unfaced edge to dust.
Separate the thermal job from the fire job before picking any material. Insulation keeps heat out of structure; a fire barrier keeps flame inside a zone. One material rarely does both well, which is why qualified nacelle stacks are layered systems: core, barrier, facing, seal, each carrying its own documented data.
Show all 6 selection factors tap to expand
SOLIMIDE foam and aerogel blanket carry the thermal duty; ManniGlas paper and mica sheet carry the barrier duty; silicone and fluorosilicone elastomers close the gaps. Specifying one layer to do another layer’s job is the most common drawing error this page sees.
Read the six factors below in order. Each constrains the next: the zone temperature profile narrows the families, the fire role adds barrier plies, the weight budget pushes toward aerogel and polyimide foam, and the attachment method decides the converting format before thickness even comes up.
Zone temperature profile, continuous and transient
The first question is not the headline rating; it is the real exposure: continuous soak, transient peaks, and the radiant load from adjacent hot structure. SOLIMIDE foam covers the inlet and cowl regime; ArmaGel HT / HTL covers warm duct runs; Pyrogel XTE, rated to 650 °C service per the maker’s data, takes the hottest lagging; and the inorganic plies, ManniGlas and mica, hold the locations where radiant and flame exposure exceed what any organic foam should see.
Put the zone’s continuous and peak temperatures on the drawing, not just the material name, so the review can check margins per the TDS. [8]
Fire role: insulation, barrier, or seal
FAR 25.856(a) frames flame propagation for thermal-acoustic insulation; ISO 2685 and AC 20-135 frame fire-zone hardware tests; FAR 25.853 frames compartment interiors. Which framing applies depends on what the part IS: a blanket core, a barrier ply, or a fire-seal gasket.
The honest division: cores (SOLIMIDE, aerogel) carry maker flame data; barriers (mica, ManniGlas) carry inorganic temperature capability; seals (BISCO, kSil V-0) carry UL 94 / E162 / E662 listings. Zone qualification testing stays with the integrator; H-O converts the documented materials to the qualified drawing. [2] [3]
Weight and thickness budget
Nacelle hardware pays for mass twice: once in fuel burn, once in the cowl’s own structural sizing. That is why the families on this page exist at all: SOLIMIDE is among the lightest foams flying, and aerogel blanket delivers a given thermal resistance in a fraction of conventional lagging thickness, per the conductivity values on each TDS (ASTM C177).
The trade is real, though: thinner, lighter stacks have less mechanical forgiveness, which raises the stakes on facings and edge protection. State the thickness envelope and the mass target, and let the stack be engineered to both rather than discovering the conflict at first fit. [5]
Vibration, airflow erosion, and handling
A propulsion bay vibrates continuously, breathes high-velocity air, and gets handled on every check. Unprotected insulation edges erode; unfaced cores fray at attachment points; soft foams crush where mechanics kneel. The countermeasures are converting decisions: PTFE-coated fiberglass facings on exposed surfaces, bonded or sewn edge closures, BISCO foam cushion plies at clamp points, and rub strips at known chafe interfaces.
Durability data lives on the facing TDS, but the geometry, where the facing wraps, how edges close, comes from the drawing. Mark airflow direction and handling zones so the facing layout protects the edges that actually take the abuse. [13]
Fluid exposure at seals and surfaces
Engine bays mist fuel, oil, and hydraulic fluid, and the difference between a gasket that lasts and one that swells out of its groove is chemistry, not firmness. Dry-side gaskets stay on BISCO silicone foam or kSil V-0 economics; anything in the mist or drip path moves to fluorosilicone sponge, the AMS 3323 family, whose fluid resistance relative to standard silicone is the reason it exists.
Surfaces follow the same logic: PTFE-coated fiberglass sheds fluids that would wick into bare glass cloth. Classify each seal location by what can reach it (continuous, mist, or none) and confirm pairings against the fluid specification on the program. [14]
Attachment, serviceability, and kitting
How the part attaches decides its converted format: bonded cores need lamination-ready surfaces and PSA selection; lace-on duct wraps need reinforced edges and grommet patterns; removable APU blankets need facings that survive repeated handling; fire seals need retention the zone test was run with. And because nacelle insulation installs as dozens of parts per ship set, kitting in installation order is what turns a drawing package into a repeatable line process.
H-O converts to all of these formats, die-cut, kiss-cut on liner, slit, laminated, kitted, with lot-coded material traceability behind each. Specify attachment method and service expectations on the drawing; format follows.
Specification Tools
Two tools to take you from “I have a propulsion-zone insulation problem” to here’s what to put on the drawing: a layer-stack explorer that walks the three classic nacelle stack-ups layer by layer, and a side-by-side comparison matrix of every material family on this page.
1. Nacelle insulation layer-stack explorer
Pick one of the three classic propulsion-zone stack-ups, then click any layer to see its job, the material families that fill it, and the watch-out that costs programs the most. Qualitative, per the H-O application research and the material TDS; the qualified stack on your program drawing governs.
Click a layer above to inspect it
Each stack renders outer layer first. The detail card returns the layer’s job, the material families H-O converts for it, and the integration watch-out.
2. Side-by-side: propulsion-zone material matrix
Every material family called out on this page, with its construction, fire-data framing as reported on its TDS, and the zone it fits. Click a column header to sort. Click any material name to jump to its accordion entry and full TDS reference.
| Material | Construction | Flame / FST data (TDS) | Key test methods | Form factor | Best for | |
|---|---|---|---|---|---|---|
| Insulation cores & lagging | ||||||
| SOLIMIDE Polyimide FoamAC-530, AC-550, AC-550H, HT-340 (25.856(a) pass per TDS) | Open-cell polyimide foam | FST data per Boyd TDS | ASTM C177; maker FST data | Inlet / cowl / APU cores | ||
| ArmaGel HT / HTLThin flexible aerogel blanket | Aerogel blanket | ASTM E84 data (TDS) | ASTM C177, C1728 | Warm bleed-duct runs | ||
| Pyrogel XTEHigh-temp industrial blanket | Aerogel blanket | ASTM E84 data (TDS) | ASTM C177, C447 | Hottest duct sections | ||
| Fire-barrier plies | ||||||
| ManniGlas Glass-Fiber Paper1200, 1900, 1902, 2000 | Inorganic glass paper | Inorganic; per TDS | Per maker TDS | Barrier / interliner plies | ||
| Phlogopite Mica SheetRigid & flexible sheet | Mineral laminate | Inorganic; per TDS | Per maker TDS | Severest fire barriers | ||
| BISCO RF-120 Heat ShieldSpecialty silicone foam | Cellular silicone | Per Rogers TDS | ASTM D1056, E162 | Radiant-shield pads | ||
| Gaskets, seals & facings | ||||||
| BISCO HT / BF Silicone FoamBF-1000/2000, HT-800/820/840/870 | Closed-cell silicone foam | UL 94 / E162 / E662 (TDS) | ASTM D1056 | Hot-zone & door gaskets | ||
| kSil V-0 Silicone SpongeSuper-soft to firm ladder | Closed-cell sponge | UL 94 V-0 (TDS) | ASTM D1056, UL 94 | V-0 compartment gaskets | ||
| Fluorosilicone SpongeAMS 3323 family | Closed-cell sponge | Per TDS | AMS 3323, ASTM D1056 | Fuel / oil mist seals | ||
| PTFE-Coated Fiberglass6085-03 to 6085-14; 6113 films | Coated glass cloth | Per TDS | Per maker TDS | Facings, wraps, rub strips | ||
Skip ahead and request your engineering review now
If your drawing already calls out a SOLIMIDE, ManniGlas, aerogel-blanket, BISCO, kSil, fluorosilicone, mica, or PTFE-fiberglass grade, send it over for engineering review.
Propulsion-zone insulation failures you can prevent at spec
Powerplant-zone material failures rarely show at delivery. The blankets fit, the seals compress, the lagging reads cool. Then a thousand flight hours later an unfaced edge has eroded to fibers, a standard-silicone gasket has swollen in the oil mist, or a crushed core is holding moisture against structure. Five patterns cover most of what fails in this zone, and each one is a specification decision made before first flight.
Propulsion-zone insulation failures are integration failures on a delay. The base materials are documented and stable; what degrades is the unprotected edge, the wrong-chemistry seal, the coverage gap at a frame. The fix is at the drawing, not at the C-check.
Show all 5 failure modes tap to expand
1. An unfaced blanket edge erodes in the airflow
A blanket core that performed perfectly at first fit starts shedding at an exposed edge: high-velocity bay airflow works the seam, fibers wick fluid, and erosion accelerates. The face sheet was specified; the edge closure was not. The fix: treat the facing as a complete envelope, PTFE-coated fiberglass faces with bonded or sewn edge closures, and mark airflow direction on the drawing so seams land out of the stream. Facing durability data is per the TDS; seam placement is design. [13]
2. Standard silicone sponge in the oil-mist path
An access-panel gasket goes in on standard silicone sponge because it sealed beautifully at build. Months of fuel and oil mist later, the gasket near the drain path has swollen and softened, and the panel weeps. Silicone elastomers are a poor long-term match for fuel and oil exposure; that is exactly the gap the fluorosilicone family (AMS 3323) exists to fill. The fix: classify every seal location by what can reach it: dry locations stay on silicone economics; mist and drip paths move to fluorosilicone sponge. [14]
3. Warm-line lagging grade on the hottest duct section
One aerogel grade gets specified across the whole bleed system because it performed on the run that was measured. The section nearest the engine runs hotter, the binder system ages faster than planned, and the lagging embrittles at the hot end. The fix: lagging grade follows the line temperature, section by section: ArmaGel HT / HTL on warm runs, Pyrogel XTE, rated for service to 650 °C per the maker’s data, on the hottest sections. Put per-section line temperatures on the drawing and let the grade split follow. [8]
4. A fire seal that took compression set
A fire-seal gasket on a daily-access door reads fine at installation and fails its compression check two years in: the material took a permanent set and the sealing force is gone, exactly where the fire strategy assumed a closed gap. The fix: for high-cycle fire-seal locations, specify silicone-class materials with compression-set data per ASTM D1056 on the TDS (BISCO HT series, kSil V-0), match firmness to the real closure force, and treat any organic foam without set data as disqualified for the location. [6]
5. Interior-grade flammability framing on a fire-zone part
A material with strong compartment-interior credentials (FAR 25.853 framing) gets carried into a designated fire zone on the assumption that “flame-rated is flame-rated.” The framings are different tests for different jobs: 25.853 addresses interior flammability, 25.856 addresses insulation flame propagation and burnthrough, and fire-zone hardware is tested per ISO 2685 / AC 20-135 campaigns owned by the integrator.
The fix: name the part’s fire role and governing framing on the drawing, and let materials carry only the data their TDS actually shows. [1] [2]
Material reference
Detailed reference for the ten material families on this page: the insulation cores (SOLIMIDE polyimide foam), the duct lagging grades (ArmaGel HT / HTL, Pyrogel XTE), the fire-barrier plies (ManniGlas glass-fiber paper, phlogopite mica, BISCO RF-120 heat shield), the gaskets and seals (BISCO HT / BF silicone foam, kSil KSV V-0 sponge, R10490 fluorosilicone sponge), and the protection layer (PTFE-coated fiberglass).
Thermal conductivity is tested per ASTM C177, compression-deflection per ASTM D1056, and flame data per UL 94 / ASTM E162 / E662 as listed on each TDS.
H-O die-cuts and converts all of them to drawing; per-grade values are per the TDS on file, not headline numbers.
SOLIMIDE Polyimide Foam (AC-530, AC-550, AC-550H, HT-340)Ultra-light insulation cores · inlet, cowl & APU bays · FST data per Boyd TDS
Specify SOLIMIDE where mass and documented FST behavior drive the pick, and protect it: the foam is light because there is almost nothing there, so facings and edge closures are part of the spec, not an option. Per-grade values are per the Boyd TDS on file.
ArmaGel HT / HTL Aerogel BlanketWarm bleed-duct lagging · thin flexible wrap · ASTM C177 per TDS
ArmaGel buys thickness margin: a given thermal resistance in a fraction of conventional lagging depth, which is what keeps insulated lines inside crowded bays. On the hottest sections step up to Pyrogel XTE; design thickness from the TDS conductivity values for your line.
Pyrogel XTE Aerogel BlanketHottest duct sections · max use temp 650 °C (1200 °F) per Aspen Aerogels Pyrogel XTE TDS (ASTM C447) · ASTM C177 per TDS
Pyrogel XTE brings industrial high-temperature headroom to airborne duct lagging: the margin lives in the material rather than the installation. Specify it section by section where the line runs hottest, and keep the warm runs on ArmaGel economics.
ManniGlas Glass-Fiber Paper (1200, 1900, 1902, 2000)Inorganic barrier & interliner plies · high-temperature stability per TDS
ManniGlas is the lightweight inorganic ply that lets a stack add fire and thermal margin without mica thickness everywhere. Ply order in a barrier stack is part of the qualified design: convert to the drawing exactly.
Phlogopite Mica Barrier SheetSeverest fire-barrier locations · rigid & flexible sheet · per maker TDS
Mica does the work no foam can, and asks for converting discipline in exchange: clean die-cutting at holes and edges, careful handling, and lamination where the stack needs support. Specify phlogopite where the exposure is most severe; muscovite covers less extreme duty.
BISCO RF-120 Heat Shield FoamRadiant-shield pads · specialty silicone foam · per Rogers TDS
RF-120 is the specialty answer for radiant-shield pads; it supplements an inorganic barrier strategy rather than replacing it. Per-grade flame and smoke data are on the Rogers TDS on file.
AeroZero Polyimide-Aerogel Film & Laminates (Blueshift)Ultra-thin polyimide-aerogel barrier ply · engine-area & harness duty · per maker TDS
BISCO HT / BF Silicone Foam (BF-1000 / BF-2000, HT-800 / 820 / 840 / 870)Hot-zone & access-door gaskets · ultra-soft to firm · ASTM D1056 per TDS
Specify silicone foam where the joint cycles and runs warm: compression-set behavior across temperature is the property that keeps the seal alive. Match the grade to the real closure force so the gasket works at mid-deflection; per-grade values are per the Rogers TDS on file.
kSil V-0 Flame-Resistant Silicone SpongeUL 94 V-0 per TDS · fire-seal & compartment gaskets · super-soft to firm
The flame rating is the gate: when V-0 is called out, unrated foams leave the candidate list at any price. The wide firmness ladder covers light covers through firmly latched panels without changing chemistry; verify the listing at your specified thickness during drawing review.
Fluorosilicone Sponge (AMS 3323 Family)Fuel / oil / hydraulic mist seals · chemical-resistant sponge · AMS 3323 per TDS
Fluorosilicone buys chemical resistance at a premium over standard silicone, so spec it where the exposure actually is: the mist and drip paths, not every gasket in the bay. Confirm fluid pairings against the program’s fluid specification; cellular values are per the TDS on file.
PTFE-Coated Fiberglass (6085 Series; 6113 PTFE Films)Facings, wraps & rub strips · erosion and fluid protection · per maker TDS
The protection layer is part of the insulation spec: PTFE-coated fiberglass keeps airflow, fluids, and handling from consuming the stack underneath. Specify the facing extent and edge closures on the drawing, and let the 6085 thickness ladder match the abuse level per the TDS.
Engine bay & nacelle insulation: engineer-grade FAQ
Twelve of the questions we hear most from propulsion, nacelle, and APU engineers and from aerospace purchasing teams. If your question isn’t here, send a drawing or call, engineering picks up.
What insulation goes inside a jet engine nacelle?
Layered stacks, not a single material. The thermal core in inlet and fan-cowl bays is typically SOLIMIDE polyimide foam, an ultra-light foam whose flame, smoke, and toxicity data is documented on the maker’s TDS and commonly evaluated against the FAR 25.856(a) flame-propagation requirement. Around it sit the supporting layers: ManniGlas or mica barrier plies where the fire strategy calls for them, a PTFE-coated fiberglass facing against erosion and handling, and silicone-foam edge gaskets where the blanket meets structure. [10]
What insulates a bleed-air duct?
Aerogel blanket, picked by line temperature. ArmaGel HT / HTL is the thin flexible default for warm runs; Pyrogel XTE, rated for service to 650 °C per the maker’s data, takes the hottest sections nearest the engine. Both die-cut into fitted sleeves, saddles, and flange collars, and both report conductivity per ASTM C177 on their TDS, which is where design thickness comes from. Add a PTFE-coated fiberglass facing where airflow erosion or repeated handling demands it. [5]
Is thermal insulation the same as a fire barrier?
No, and treating them as interchangeable is the most expensive confusion in this zone. Insulation (polyimide foam, aerogel blanket) limits heat transfer to structure; a fire barrier (mica sheet, glass-fiber paper, layered with heat-shield silicone) resists flame and radiant exposure as part of a containment strategy tested per ISO 2685 / AC 20-135 campaigns. Qualified nacelle stacks layer the two jobs; a drawing should name which job each ply carries. [3]
What does FAR 25.856 actually require of insulation materials?
FAR 25.856 addresses thermal-acoustic insulation in transport-category aircraft: paragraph (a) frames flame-propagation behavior and paragraph (b) frames burnthrough resistance, each tied to test methods in Part 25’s appendices. This page cites the rule qualitatively: materials like SOLIMIDE carry the relevant test data on the maker’s documentation, and showing compliance for an installation belongs to the airframer’s certification process, not to a converter. H-O’s role is converting the documented material to the qualified drawing. [2]
Which gasket material survives next to an engine?
For dry hot-zone gaskets, closed-cell silicone foam (BISCO BF / HT series) and kSil V-0 sponge are the working families: silicone-class temperature capability, compression-set behavior that survives cycling, and UL 94 / E162 / E662 data per grade on the TDS. Where fuel, oil, or hydraulic mist can reach the seal, step to fluorosilicone sponge (AMS 3323 family). The chemistry call comes before the firmness call. [9]
When does a seal need fluorosilicone instead of silicone?
When the seal lives in the fuel, oil, or hydraulic mist path. Standard silicone elastomers are a poor long-term match for those exposures: they swell and soften where mist and drips collect. Fluorosilicone sponge, the AMS 3323 family, holds its properties in exactly those locations, which is why APU access doors and drain-path seals move to it while dry-side gaskets stay on standard silicone economics. Classify each location by what can reach it and confirm against the program’s fluid specification. [14]
Why use aerogel blanket instead of conventional duct lagging?
Thickness. Aerogel blankets deliver a given thermal resistance in a fraction of conventional lagging depth, per the ASTM C177 conductivity values on their TDS, and propulsion bays are exactly where that matters: crowded routing, tight cowls, and personnel-protection surface-temperature targets. The trade is mechanical delicacy, which the facing layer answers. Where thickness is free, conventional lagging can win on cost; in a nacelle, thickness is never free. [8]
What protects insulation from airflow erosion and handling damage?
A facing layer, specified as part of the stack: PTFE-coated fiberglass faces and wraps with bonded or sewn edge closures, plus die-cut rub strips at known chafe points and thin silicone-foam cushion plies at clamp and contact locations. Erosion starts at unsealed edges and seams rather than face sheets, so the closure detail matters as much as the facing material. Mark airflow direction and handling zones on the drawing. [13]
Can H-O supply complete nacelle insulation kits?
Yes. The deliverable that makes ship-set installation repeatable is the kit: every core, ply, facing, gasket, and rub strip die-cut to drawing, labeled, and packed in installation order, with lot-coded material traceability behind each part. H-O die-cuts, kiss-cuts on liner, slits, laminates multi-layer stacks, and kits across all ten families on this page as an ISO 9001:2015 certified organization in Winsted, Connecticut.
Does H-O certify parts for fire zones or hold flight qualification?
No, and a converter that claims to should worry you. Fire-zone qualification (ISO 2685 / AC 20-135 campaigns), insulation compliance findings under FAR 25.856, and airworthiness sign-off belong to the airframer, the propulsion integrator, and their test houses. H-O’s role is precise and bounded: convert the documented materials to the qualified drawing, repeatably, with material traceability and lot-code TDS records that support your certification file. [4]
Why does this page frame values as “per the TDS on file”?
Because the honest number depends on grade, thickness, temperature, and compression, and a single headline figure flatters one condition while misleading the rest. This page names the governing test methods, ASTM C177 thermal conductivity, ASTM D1056 compression-deflection, UL 94 / E162 / E662 flame data, AMS 3323 for fluorosilicone, and keeps per-grade values on the manufacturer TDS, which H-O reviews against your drawing during quoting. [6]
How do orders run for made-to-order nacelle components?
Send a drawing, BOM, or sample part. Engineering reviews the material call-outs against the TDS layer and your zone conditions, then quotes prototype and production. Everything is made-to-order against the drawing; MOQ varies by material and part. Samples typically ship in 3–5 business days for common die-cut configurations on materials we keep on hand, and standard production runs ship about 2 weeks after drawing approval, with expedited service available. Lead-time details live in the process strip above and the quote form below.
Glossary: terms used on this page
Quick reference for the propulsion-zone, insulation, and fire-protection terminology used throughout. Each entry links to the relevant test method or section where applicable.
Nacelle
The aerodynamic housing around an engine: inlet barrel, fan cowl doors, thrust reverser, and exhaust hardware. For converted materials it is a set of bays with different temperature, fire, and erosion exposures, each carrying its own insulation stack.
Designated fire zone
A region of the aircraft, engine compartments and APU bays among them, where regulations require specific fire detection, extinguishing, and containment provisions. Hardware in these zones is tested per fire-resistance methods framed by ISO 2685 [3] and AC 20-135 [4].
Firewall
The barrier structure isolating a fire zone from the rest of the airframe. The converted parts in a firewall strategy split into barrier plies (mica, glass-fiber paper) and compliant fire seals (silicone-class foams and sponges) that close gaps at panels and penetrations.
FST (flame, smoke, toxicity)
The trio of fire-behavior properties aerospace interiors and insulation are evaluated against: how a material burns, how much smoke it generates, and what its combustion releases. FST data lives on each material’s TDS; the applicable test framing depends on the part’s role and location.
FAR 25.856(a) / (b)
The U.S. transport-category airworthiness rule for thermal-acoustic insulation: paragraph (a) frames flame propagation, paragraph (b) frames burnthrough resistance, with test methods in the Part 25 appendices. Cited qualitatively on this page; compliance findings belong to the airframer. [2]
Bleed air
Hot compressed air extracted from the engine for anti-ice, pressurization, and pneumatic systems, carried through ducting that runs near structure, wiring, and maintenance access. Bleed-duct lagging exists to protect all three, and its grade follows the line temperature.
Aerogel blanket
Flexible insulation made by reinforcing silica aerogel, among the lowest-conductivity solid insulations, with a fiber batt. It delivers a given thermal resistance in a fraction of conventional thickness; conductivity is tested per ASTM C177 [5]. This page’s grades are ArmaGel HT / HTL and Pyrogel XTE.
Polyimide foam
An ultra-light open-cell foam chemistry (SOLIMIDE on this page) used as aircraft thermal-acoustic insulation cores. Its value is mass and documented FST behavior; its converting requirement is protection, facings and edge closures, because there is almost no material in the material.
Compression set
The permanent deflection a foam or sponge retains after sustained compression, the property that quietly kills access-door and fire-seal gaskets. Silicone-class materials hold low set across temperature; set data is reported per ASTM D1056 [6] on each TDS.
Lagging / facing
Lagging is the insulation wrapped around a duct or line; the facing is the protective outer layer over an insulation stack. On this page lagging is aerogel blanket die-cut to the line, and facings are PTFE-coated fiberglass with engineered edge closures.
AMS 3323 (fluorosilicone sponge)
The SAE Aerospace Material Specification family covering closed-cell fluorosilicone sponge, the fuel- and chemical-resistant sibling of silicone sponge. On this page it marks the gasket chemistry for fuel, oil, and hydraulic mist paths. [14]
Last updated · Reviewed by H-O Products engineering (ISO 9001:2015 certified converter, Winsted, CT).
Standards, test methods & technical references
The standards, test methods, and vendor technical data sheets cited throughout this page. Standards editions current as of June 2026; verify against the publishing body before final spec. H-O converts materials that are tested to these methods on the source manufacturer’s TDS; H-O does not independently certify materials, and flight qualification remains with the airframer or system integrator.
FAR 25.853 (14 CFR 25.853)
Compartment interiors flammability requirements for transport-category airplanes, with test methods in Part 25 Appendix F. Cited qualitatively as the framing for interior-adjacent materials; compliance findings belong to the certificate holder. ecfr.gov (25.853)
FAR 25.856 (14 CFR 25.856)
Thermal / acoustic insulation requirements: paragraph (a) flame propagation and paragraph (b) burnthrough resistance, with methods in Part 25 Appendix F Parts VI / VII. Cited qualitatively; installation compliance belongs to the airframer. ecfr.gov (25.856)
ISO 2685
Aircraft – Environmental test procedure for airborne equipment – Resistance to fire in designated fire zones. The international framing for fireproof / fire-resistant hardware testing, cited by designation. iso.org (ISO 2685)
FAA AC 20-135
Advisory Circular: Powerplant Installation and Propulsion System Component Fire Protection Test Methods, Standards, and Criteria. The U.S. guidance for fire-zone test campaigns, cited by designation; the campaign belongs to the integrator. faa.gov (AC 20-135)
ASTM C177
Standard Test Method for Steady-State Heat Flux Measurements and Thermal Transmission Properties by Means of the Guarded-Hot-Plate Apparatus. The conductivity method behind the aerogel and foam thermal values on the TDS. astm.org/c0177
ASTM D1056
Standard Specification for Flexible Cellular Materials, Sponge or Expanded Rubber. The compression-deflection and compression-set framework behind the silicone foam, sponge, and fluorosilicone grades on this page. astm.org/d1056
UL 94
Standard for Tests for Flammability of Plastic Materials for Parts in Devices and Appliances. The V-0 listings cited on the kSil and silicone-foam TDS; listings are per grade and thickness. shopulstandards.com (UL 94)
Aerogel blanket technical data sheets (Armacell ArmaGel; Aspen Aerogels Pyrogel XTE)
Manufacturer TDS for the two lagging grades on this page: thermal conductivity per ASTM C177, surface burning per ASTM E84, C-series insulation methods per grade, and the Pyrogel XTE maximum use temperature of 1200 °F (650 °C) determined per ASTM C447 (Estimation of Maximum Use Temperature). armacell.com · aerogel.com
Rogers BISCO technical data sheets
Manufacturer TDS for the BISCO BF / HT silicone foams and the RF-120 heat-shield grade: compression-deflection per ASTM D1056, UL 94 listings, and ASTM E162 / E662 flame and smoke data per grade. rogerscorp.com
Boyd SOLIMIDE polyimide foam technical data
Manufacturer data for the SOLIMIDE aerospace grades (TA-301, AC-series, HT-340): density, thermal conductivity per ASTM C177-class methods, and flame / smoke / toxicity test data per grade. boydcorp.com
Lydall (Alkegen) ManniGlas technical data
Manufacturer data for ManniGlas glass-fiber papers (1200 / 1900 / 1902 / 2000): basis weight, thickness, and high-temperature stability per grade. alkegen.com
Mica barrier sheet technical data (muscovite / phlogopite)
Maker TDS for rigid and flexible mica sheet: temperature capability, dielectric data, and forming limits per grade; phlogopite grades carry the highest temperature capability. cogebi.com
PTFE-coated fiberglass technical data (6085 / 6113 series), TDS on file
Per-grade data for the PTFE-coated fiberglass facing series and skived PTFE films converted by H-O: thickness ladder, tensile and temperature capability, and surface properties, per the TDS on file with H-O.
SAE AMS 3323
SAE Aerospace Material Specification for fluorosilicone sponge. Cited on the fluorosilicone sponge TDS; the family this page maps to fuel / oil / hydraulic mist seal locations. sae.org (AMS 3323)
Updated . Standards editions and links current at publication; verify against the publishing body before final spec. H-O converts materials tested to the methods cited; lot-specific documentation available on request.
Get a nacelle insulation engineering quote
Send a drawing, BOM, or spec sheet. We typically respond within one business day with a material-family recommendation, prototype lead time, and TDS verification against your zone temperatures, fire role, fluid exposure, and attachment method.
Prefer to talk it through first? Contact the engineering team or call (860) 469-1144.
See also: related H-O application pages
Engineering content for the adjacent aerospace application categories, all under the aerospace, defense & space industry hub and the thermal management & insulation overview.
Application page
Fuselage, cabin & ECS thermal insulation
The airframe side of aircraft insulation: fuselage blanket cores, moisture control, and ECS duct insulation forward of the firewall.
Read the page
Application page
FST-compliant materials for aircraft
The fire, smoke, and toxicity layer in depth: insulation flame propagation, fire-rated gaskets, and inorganic barrier materials.
Read the page
Application page
Fuel, hydraulic & chemical-zone sealing
The fluid-side chemistry in depth: fluorosilicone, FKM, and the seal families for fuel and hydraulic systems.
Read the page
Application page
Aircraft vibration, NVH & shock isolation
Isolation mounts, damping pads, and the vibration-control materials that share these bays with the insulation.
Read the page
Application page
Avionics thermal management & interface materials
Conduction-cooled electronics: graphite heat spreaders, TIM pads, and dielectric films for the boxes the nacelle feeds.
Read the page
Industry hub
Aerospace, defense & space materials
The full industry directory: every aerospace sub-application H-O converts for, from thermal insulation to EMI shielding.
Open the hub
Material data & standards. All material properties and ratings referenced on this page are taken from the source manufacturer’s technical data sheets and the cited standards: thermal conductivity per ASTM C177, compression-deflection per ASTM D1056, flammability listings per UL 94 and ASTM E162 / E662 as listed per grade and thickness, fluorosilicone sponge per the AMS 3323 family, and FAR 25.853 / 25.856 and ISO 2685 / AC 20-135 cited qualitatively as regulatory framing.
This page frames performance qualitatively and keeps per-grade values on the TDS, where they belong. H-O converts materials tested to these methods; H-O does not independently certify materials, does not perform fire-zone qualification, and makes no airworthiness or flight-certification claims. Verify against the vendor TDS and your program’s certification basis for your specific application.
Conversion scope. H-O die-cuts and converts sheet, roll, and blanket stock to drawing in Winsted, Connecticut: die-cut and kiss-cut-on-liner gaskets, profiled insulation cores, fitted lagging sleeves and wraps, laminated multi-layer barrier stacks, and installation-ordered kits, with material traceability and lot-code TDS records, as an ISO 9001:2015 certified organization.
H-O does not manufacture raw material in-house; extruded or molded profiles are coordinated through a partner network. Lead-time and MOQ details are on the process strip and in the quote form above.