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SOLIMIDE, ManniGlas, BISCO Silicones, or Nomex: Choosing FST-Documented Materials for Aircraft Interiors
FST stands for flame, smoke, and toxicity, and on a transport-category aircraft those three words decide which materials are allowed inside the pressure vessel. The catch is that FST is not one requirement: FAR 25.853 governs cabin-interior materials, FAR 25.856 governs thermal and acoustic insulation, and each clause points at different test methods and different material families.
This guide walks the families on the H-O FST-compliant materials page, from SOLIMIDE polyimide foam at the top of the insulation ladder to ManniGlas inorganic paper, the BISCO fire-block silicones, and the Nomex aramid system, with every claim hedged the way the paperwork demands: data lives on each grade's TDS, and compliance determinations belong to your program.
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Which clause is your part actually specified against?
Material selection goes wrong fastest when a buyer asks for "FST foam" without naming the clause. A cabin sidewall pad and a fuselage insulation blanket both burn in the same fire, but the regulation reads them differently: interior finish materials are commonly evaluated to the FAR 25.853 Bunsen-burner methods, while thermal and acoustic insulation installed in the fuselage is commonly evaluated to the FAR 25.856 radiant-panel method, with FAR 25.855 covering cargo-compartment liners.
Smoke density (ASTM E662) and operator toxicity requirements ride alongside, and a grade that satisfies one clause has not automatically satisfied another. The families below are sorted by the duty they usually serve, and the clause language stays qualitative on purpose; the test reports belong to the material maker and your certification chain.
SOLIMIDE polyimide foam: the insulation-ladder anchor
SOLIMIDE polyimide foam (AC-530, AC-550, HT-340, TA-301) is the light, open-cell insulation family the aircraft industry reaches for when weight, thermal performance, and fire behavior all matter at once. The AC grades serve general thermal-acoustic duty, HT-340 carries the maker's elevated-temperature designations, and TA-301 emphasizes acoustic absorption; thermal conductivity per ASTM C177 / C518 and acoustic data per ASTM C423 are reported on each TDS.
H-O die-cuts and kits SOLIMIDE into blanket inserts, gap fillers, and shaped lay-ins; the foam's low density rewards careful nesting, and its grades are commonly evaluated to the FAR 25.856 insulation context by the programs that specify it.
ManniGlas glass-fiber paper: the inorganic facing and backer
Where the requirement says "does not burn" rather than "burns slowly," organic chemistry runs out of road. ManniGlas glass-fiber paper (1200, 1900, 2000) is the inorganic answer: a non-combustible glass paper that serves as facings, fire barriers, and backing layers behind decorative surfaces, with thermal data per ASTM C177 on the TDS. It pairs naturally with the foams: a ManniGlas facing carries the fire-side duty while a lighter foam carries the thermal duty, and H-O laminates the two into one die-cut part where the drawing allows.
BISCO silicones: fire-block, sponge, and barrier duty
The silicone family covers three distinct jobs. BISCO RF-120 and FPC fire-block grades are the heat-shield and fire-block specialists, sitting beside hot zones and across fire paths. BISCO RS flame-retardant silicone sponge is the gasketing workhorse of the fire-documented world in joint-strip and seal duty, and kSil V-0 grades from the kSil V-0 silicone sponge family carry UL 94 V-0 file classes with ASTM E162 / E662 data per TDS.
For acoustic mass, the BISCO A2 sound barrier adds limp-mass attenuation with fire-documented silicone chemistry, including a fiberglass-reinforced version (A2 reinforced) where handling strength matters.
Nomex aramid system: paper, calendered, high-density, pressboard
The Nomex family spans 410 standard paper, 411 calendered, 414 high-density, and 818 pressboard: inherently flame-resistant aramid that does not melt or drip, with dielectric data per the maker's TDS. In FST-sensitive zones it serves as wire-way liners, barrier layers, and insulation spacers where a paper form factor beats a foam. The grades differ in density and stiffness rather than chemistry, so the drawing usually picks the calender state, and H-O die-cuts all four.
ENSOLITE vinyl nitrile and the trim-foam question
Ordinary trim pads, spacers, and anti-rattle parts still need documentation when they live in the cabin. ENSOLITE vinyl nitrile includes grades whose TDS references the FAR 25.853 test context, which is exactly what a cabin-trim drawing wants to see: a closed-cell elastomeric foam with ASTM D1056 mechanical data and fire documentation on the same sheet. It is the family to name when the part is a pad first and a fire question second.
PTFE-coated fiberglass: the high-temperature surface layer
Where an FST-documented stack also needs a slick, high-temperature surface (wear faces, release surfaces, wire-way rub strips), PTFE-coated fiberglass in the 6085 series adds an inorganic glass carrier with a PTFE surface. It is commonly specified as the contact layer over a compliant core rather than as the insulation itself.
FST-Documented Families by Duty
| Family | Usual duty | Clause context (qualitative) | Documentation on TDS |
|---|---|---|---|
| SOLIMIDE polyimide foam | Thermal-acoustic insulation | Insulation duty; commonly evaluated to FAR 25.856 context | ASTM C177 / C518 thermal; C423 acoustic |
| ManniGlas glass-fiber paper | Inorganic facing / barrier | Non-combustible layer in either context | ASTM C177; maker fire documentation |
| BISCO RF-120 / FPC | Fire block / heat shield | Fire-path and hot-zone duty | Maker fire-block data; ASTM D1056 mechanical |
| BISCO RS sponge / kSil V-0 | Gaskets and seals | Interior seal duty with fire documentation | UL 94 classes; ASTM E162 / E662 per grade |
| Nomex 410 / 411 / 414 / 818 | Liners, spacers, wraps | Flame-resistant aramid, paper form factors | Maker dielectric and thermal designations |
| ENSOLITE vinyl nitrile | Trim pads and spacers | Grades referencing the FAR 25.853 context | ASTM D1056; fire documentation per grade |
| PTFE-coated fiberglass 6085 | Surface / wear layer | Contact layer over a compliant core | Maker temperature and surface designations |
Illustrative and relative only; confirm each grade on its current technical data sheet. Clause assignments are qualitative descriptions of common usage, not compliance findings; this article quotes no test results.
How do smoke and toxicity reshape the shortlist?
A material can pass a flame test and still be the wrong answer for an occupied pressure vessel, because the second and third letters of FST are their own gates. Smoke density per ASTM E662 and the toxicity screens that operators layer on top tend to thin organic candidate lists quickly, which is why the inorganic and inherently flame-resistant families (ManniGlas, Nomex, the fire-block silicones) hold so much cabin territory.
The practical sequence: name the clause, then ask which candidates carry smoke and toxicity lines on the TDS, then compare mechanical properties among the survivors. Run the sequence backward and you will shortlist a mechanically perfect foam that the documentation review later removes.
How H-O Products helps
H-O Products die-cuts, waterjet-cuts, laminates, and kits; we do not manufacture foam, paper, or silicone in-house. What we do in Winsted, Connecticut is precision conversion of the families above to your drawing: SOLIMIDE blanket inserts nested for yield, ManniGlas facings laminated to foam cores, BISCO RS and kSil V-0 gaskets cut with adhesive backings, and Nomex liners slit and kitted to work orders, all under our ISO 9001:2015 certified quality management system with lot-coded material traceability and the maker's TDS carried on the order.
Frequently asked questions
What does FST mean on an aircraft material spec?
Flame, smoke, and toxicity: the three behaviors a material must keep within limits inside an occupied aircraft. Flame behavior for interior materials is commonly evaluated to the FAR 25.853 methods, insulation to the FAR 25.856 radiant-panel context, smoke density to ASTM E662, and toxicity to the screening programs operators and airframers maintain. The exact requirement set depends on where the part lives, so the clause reference on the drawing is the first thing to confirm.
Which material family is the usual starting point for fuselage insulation?
SOLIMIDE polyimide foam, because it combines very low density with thermal data per ASTM C177 / C518 and acoustic data per ASTM C423 on the TDS, and its grades are commonly evaluated to the insulation clause context. ManniGlas glass-fiber paper rides alongside as the inorganic facing or fire-barrier layer, and the two are often laminated into one die-cut blanket component.
Can H-O certify a part as FAR 25.853 or 25.856 compliant?
No, and no converter can. Compliance findings belong to your program's certification process; what H-O provides is the converted part, the maker's TDS and fire documentation for the exact grade and lot supplied, and traceability under our ISO 9001:2015 certified quality management system. That package is what your certification chain needs to make its finding.
What if my part needs fire documentation and gasket mechanics at the same time?
That is the BISCO RS and kSil V-0 territory: flame-retardant silicone sponges with UL 94 classes and, on specific grades, ASTM E162 / E662 data per TDS, plus the compression behavior a seal actually needs (ASTM D1056). For trim and anti-rattle duty, ENSOLITE vinyl nitrile grades that reference the FAR 25.853 context cover the same dual requirement in a lower-temperature, lower-cost foam.
Get an FST material recommendation
Tell us where the part lives (cabin, insulation, cargo, wire-way), the clause your drawing references, and the mechanical job (insulate, seal, pad, line), and we will recommend a family and grade direction and quote converted parts to your drawing.
Samples typically ship in 3 to 5 business days for common die-cut configurations on materials we keep on hand; standard production runs about two weeks after drawing approval; expedited service is available. MOQ varies by material and part.
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Last updated · Reviewed by H-O Products engineering (ISO 9001:2015 certified converter, Winsted, CT).
References
- FAR 25.853 (compartment interiors, flammability of interior materials); FAR 25.855 (cargo and baggage compartments); FAR 25.856 (thermal/acoustic insulation materials). Cited by designation, qualitatively; test findings belong to program certification.
- ASTM E662 (specific optical density of smoke); ASTM E162 (surface flammability under radiant heat); UL 94 (flammability classes, per grade TDS).
- ASTM C177 / C518 (thermal conductivity); ASTM C423 (acoustic absorption); ASTM D1056 (flexible cellular materials).
- Manufacturer technical data sheets: SOLIMIDE polyimide foam grades, ManniGlas glass-fiber paper, BISCO RF-120 / FPC / RS / A2 silicones, kSil V-0 silicone sponge, Nomex aramid paper and pressboard, ENSOLITE vinyl nitrile, PTFE-coated fiberglass 6085 series.
This article summarizes FST material-selection principles using the families and published method designations cited on the parent application page. Comparisons are qualitative; classes and values are per each grade's current technical data sheet, and no test results are quoted. Regulatory clauses are named for orientation only: compliance findings belong to your program's certification process, and H-O makes no airworthiness or compliance determinations.
All parts are custom manufactured to order; minimum production run quantities vary by material and part. H-O is a converter, not a raw-material producer.