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Aerogel, Polyimide Foam, or Mica: Selecting Insulation by Conductivity, Outgassing, Flame, and Dielectric Strength
No single insulation material wins every job, so the right one is the lowest-conductivity material that also clears the secondary constraint your application actually has, outgassing, flame, dielectric strength, or peak temperature.
Silica aerogel gives the lowest conductivity in the least thickness; polyimide foam wins where lightweight, flame-char behavior, and low outgassing matter together; and mica or glass-fiber paper win as thin high-temperature electrical barriers. This guide separates the four properties that decide the choice and the standards that measure each, so the selection is made on evidence rather than habit.
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The application problem
Insulation does the opposite job from a thermal interface material: instead of carrying heat across a joint, it holds heat back, minimizing the flow from a hot side to a cold side.
That shows up in a wide span of parts H-O Products converts: aerogel or polyimide foam wrapping a duct, pipe, or process vessel; lightweight foam insulating an aircraft fuselage, cabin, or cargo bay; a cryogenic-grade blanket on an LNG or cold-box line; a thin mica or glass-fiber layer insulating a coil from a core or a busbar from a frame at high temperature; and aerogel or mica acting as a fire barrier between battery cells.
The failure that follows from a poor choice depends on which constraint was missed. Pick on conductivity alone and you can end up with a material that fogs an optical surface in vacuum, degrades a flame-rated assembly, breaks down electrically next to a live part, or simply cannot survive the peak temperature. The number that mattered was not always the conductivity; it was the constraint hiding behind it.
So the discipline is to identify the controlling secondary requirement first, then choose the lowest-conductivity material that satisfies it within the thickness and weight you can spend.
The four properties that decide the choice
Four measurable properties, each with a governing test method, separate these materials. Treat each as a test the candidate is evaluated against on the manufacturer’s data sheet, not as a guarantee the converter owns.
- Thermal conductivity, measured per ASTM C177. The steady-state guarded-hot-plate method gives the conductivity in W/m·K that sets how much insulation you need for a given heat flow. Lower conductivity means less thickness for the same job, which is decisive when space or weight is tight. Silica aerogel is commonly cited among the lowest conductivities of any solid; confirm the grade value on the data sheet.
- Outgassing, screened per ASTM E595. In vacuum, a material can release volatiles that condense on cold optical or sensor surfaces. The E595 screen measures total mass loss (TML) and collected volatile condensable material (CVCM) after 125 C for 24 hours under vacuum, with a common screening threshold of TML at or below 1.0 percent and CVCM at or below 0.10 percent. Space, sealed-optics, and vacuum hardware live or die on this.
- Flammability, classified per UL 94. Flame-controlled assemblies often require a UL 94 class such as V-0 on the material, and the class is grade- and thickness-specific. Polyimide foam is notable for charring rather than burning, which is why it appears in aircraft interiors and other flame-sensitive enclosures.
- Dielectric strength, measured per IEC 60243. When the insulation also has to keep two conductors apart, dielectric strength in kV/mm matters. Mica is a classic high-temperature dielectric, and thin polyimide film is the dielectric carrier in flexible heaters and electrical insulation layers. Confirm the kV/mm and the temperature rating on the manufacturer’s data sheet.
Peak and continuous service temperature sits alongside these as a hard gate: a grade is only a candidate if it survives the temperature. Polyimide foam spans a broad range per its maker; mica tolerates high continuous temperature, with phlogopite rated higher than muscovite; glass-fiber paper handles thin high-temperature layers; and aerogel grades span from cryogenic to high-temperature industrial. Confirm continuous and peak on the grade data sheet, because the span is grade dependent.
The material families, side by side
Named as materials H-O Products converts, the insulation families divide cleanly by which constraint they win on. Grade-level conductivity, temperature, flame class, and dielectric values live on the manufacturer’s data sheet.
- Silica aerogel blanket. The lowest conductivity for the thickness and weight, which is why it wins where insulation space is constrained: ducts, pipes, and process equipment, and as a thin fire barrier between battery cells. Sector grades cover building, industrial, and rail duty, and a cryogenic grade is engineered for sub-ambient and cryogenic lines and cold boxes. Available as a general aerogel family (aerogel insulation), the sector grades (building, industrial, and rail aerogel), and the cryogenic grade (cryogenic aerogel).
- Polyimide foam. Lightweight and flame-resistant, polyimide foam chars rather than burns and is commonly used where low weight, flame behavior, and low outgassing matter together. The aerospace grade insulates fuselage, cabin, and cargo bay, is reported by its maker to exceed the FAR 25.856 flammability requirements, and is essentially non-outgassing for sealed and space hardware, which makes it a candidate against the ASTM E595 screen. Available as a general family (polyimide foam) and the aerospace grades (aerospace polyimide foam).
- Mica barrier sheet. A thin inorganic layer that insulates electrically and survives high temperature where a polymer film would not, mica is the classic high-temperature electrical barrier between a coil and a core, a busbar and a frame, or a heater element and a housing, and it also serves as a battery fire-barrier layer. Available as die-cuttable barrier sheet (mica barrier sheets).
- Glass-fiber paper. A thin, high-temperature non-woven layer for insulation and barrier duty where a flexible inorganic paper suits the geometry. Available as a converted paper family (glass-fiber paper).
- Battery thermal-runaway fire barrier. Between cells or around modules, aerogel and mica are common barrier layers that slow cell-to-cell propagation so the pack can meet propagation-safety requirements such as GB 38031 and the corresponding UN-type regulation; those are assembly-level requirements owned by the pack maker. Available as a dedicated barrier family (EV battery thermal fire barriers).
Insulation Family Comparison
| Family | Conductivity (ASTM C177) | Temperature range | Flame (UL 94) | Dielectric (IEC 60243) | Outgassing (ASTM E595) | Typically wins when |
|---|---|---|---|---|---|---|
| Silica aerogel blanket | Lowest of solids | Cryogenic to high-temp industrial | Grade dependent | Not an isolation choice | Verify grade on TDS | Thinnest insulation for the space |
| Cryogenic aerogel | Very low, sub-ambient | Engineered for cryogenic lines | Grade dependent | Not an isolation choice | Verify grade on TDS | LNG / cold-box / cryogenic lines |
| Polyimide foam | Low, lightweight | Broad span per maker | Chars, not burns | Film form is dielectric | Low-outgassing grades | Lightweight + flame + low outgassing |
| Mica barrier sheet | Not a low-k insulator | High continuous temp | Inorganic, non-burning | High-temp dielectric | Inorganic | Thin high-temperature electrical barrier |
| Glass-fiber paper | Thin layer, not low-k | Thin high-temperature layers | Inorganic, non-burning | Insulating non-woven | Inorganic | Thin high-temperature paper layer |
Strong Moderate / verify Not its strength Rankings are qualitative and reflect the material logic above; they are a starting point, not grade-level data.
Illustrative only; confirm against current material data and a drawing review. The rankings are qualitative directions, not measured values. Confirm conductivity, temperature, flame class, dielectric strength, and outgassing for the specific grade against the manufacturer’s current technical data sheet before specifying.
Design and converting considerations
Insulation is converted, not produced, here, and the converting choices follow the geometry and the constraint.
- Set thickness from the conductivity and the heat flow. The required thickness comes from the conductivity per ASTM C177 and the allowable heat flow; a lower-conductivity material lets you hit the target in a thinner part, which is the whole reason aerogel is chosen where space is tight.
- Cut to the outline and the geometry. Blanket and sheet stock are die-cut to print on rotary or flatbed tooling, kiss-cut on a liner where a peelable layer helps placement, and laser- or waterjet-cut for thick blocks, complex profiles, or prototypes. Outline and thickness tolerances are set on the drawing and confirmed at quote.
- Laminate the stack where one layer is not enough. A barrier often needs more than one function, for example a dielectric layer plus a thermal layer plus an adhesive and a liner, and those can be laminated into a single converted part so the assembly line places one piece.
- Respect the constraint at the cut edge. A flame-rated, low-outgassing, or dielectric requirement applies to the finished part, so adhesives, facings, and liners added in converting are chosen so they do not undermine the property the material was selected for.
- Kit and sequence for the assembly. Multiple insulation parts for one unit can be kitted and sequenced so they reach the line in the order they are installed, which matters on a multi-layer fuselage, pack, or vessel build.
Common failure modes
| Failure mode | Root cause | Consequence |
|---|---|---|
| Conductivity-only selection | Choosing the lowest-k material without checking the controlling secondary constraint | The part insulates but fails on outgassing, flame, dielectric, or temperature |
| Outgassing contamination | A high-outgassing material used in vacuum or near sealed optics | Volatiles condense on cold surfaces; the optic or sensor fogs; fails the ASTM E595 screen |
| Flammability non-compliance | A material that degrades a flame-rated assembly’s class | The assembly no longer meets its required UL 94 class or equivalent |
| Electrical breakdown | An insulation chosen for heat used where it must also isolate, without dielectric strength | Breakdown or leakage between conductors at temperature |
| Temperature overrun | A grade specified above its continuous or peak temperature rating | The material degrades, shrinks, or loses its properties in service |
| Inadequate fire barrier | A battery barrier too thin or the wrong material to slow propagation | Cell-to-cell thermal runaway propagates and the pack misses its safety requirement |
How H-O Products helps
H-O Products is a precision die-cut converter, made to order. We convert silica aerogel blanket, including sector and cryogenic grades, polyimide foam, including aerospace grades, mica barrier sheet, and glass-fiber paper into custom insulation and barrier parts built to your drawing, die-cut or kiss-cut to print, laser- or waterjet-cut for thick blocks and complex profiles, laminated into multi-layer stacks, slit to width, and kitted to your build sequence.
We do not produce the raw blanket or foam; we convert maker stock to your part. Where the choice is between aerogel, polyimide foam, mica, and glass-fiber paper, we help you reason from the controlling constraint to a material family, point you to the ASTM C177, ASTM E595, UL 94, and IEC 60243 data to confirm on the manufacturer’s current technical data sheet, and turn it into a repeatable converted part.
We work as an ISO 9001:2015 certified organization in Winsted, CT, with material data sheets, certificates of conformance, and lot traceability available on request.
Tell us the constraint, and we will narrow the material
Send us the heat-flow or conductivity target, the operating and peak temperature, and the controlling constraint, vacuum outgassing, flame class, or dielectric isolation, along with the insulation outline and thickness. We will recommend a material family direction, flag the ASTM C177, ASTM E595, UL 94, and IEC 60243 data to confirm on the data sheet, and convert a die-cut part to your footprint. Samples typically ship in 3 to 5 business days for common configurations; standard production runs about two weeks.
Family-owned in Winsted, Connecticut since 1971 · ISO 9001:2015 certified · OEMs worldwide send us a drawing — and get back their part.
Frequently asked questions
Aerogel or polyimide foam, which insulates better?
They win on different things. Silica aerogel is commonly cited among the lowest conductivities of any solid, so it gives the most insulation in the least thickness and weight, which is decisive where space is tight. Polyimide foam is lightweight and flame-resistant, charring rather than burning, and includes low-outgassing grades, so it wins where flame behavior and outgassing matter together, as in aircraft interiors and sealed hardware. Confirm grade conductivity and properties on the manufacturer’s current data sheet.
What is ASTM C177?
ASTM C177 is the steady-state guarded-hot-plate test method for the thermal conductivity of insulation, reported in W/m·K. It is the reference for how much insulation thickness a given heat-flow target requires, and it is the conductivity number to compare between insulation candidates.
Which insulation passes the vacuum outgassing screen for space hardware?
Materials that meet the ASTM E595 screen, with total mass loss at or below 1.0 percent and collected volatile condensable material at or below 0.10 percent after 125 C for 24 hours in vacuum, are the candidates for vacuum and sealed-optics hardware. Low-outgassing polyimide foam grades and certain aerogel grades are commonly evaluated against this screen; confirm the specific grade’s reported TML and CVCM on the manufacturer’s data sheet.
Why use mica instead of a polymer film for high-temperature insulation?
Because mica is an inorganic high-temperature electrical barrier that survives continuous temperatures where a polymer film would degrade, while still providing dielectric strength. It is commonly specified between a coil and a core, a busbar and a frame, or a heater element and a housing, and as a battery fire-barrier layer. Confirm the continuous temperature rating and dielectric strength on the manufacturer’s data sheet.
Can these insulation materials act as a battery thermal-runaway fire barrier?
Aerogel and mica are commonly used as fire-barrier layers between cells or around modules to slow cell-to-cell thermal-runaway propagation, helping a pack meet propagation-safety requirements such as GB 38031 and the corresponding UN-type regulation. Those requirements are assembly-level and are owned by the pack maker; H-O converts the barrier material to the drawing rather than validating the finished pack.
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Last updated · Reviewed by H-O Products engineering (ISO 9001:2015 certified converter, Winsted, CT).
References and standards
- ASTM C177 – Standard Test Method for Steady-State Heat Flux Measurements and Thermal Transmission Properties by Means of the Guarded-Hot-Plate Apparatus (insulation thermal conductivity).
- ASTM E595 – Standard Test Method for Total Mass Loss and Collected Volatile Condensable Materials from Outgassing in a Vacuum Environment (screen of TML at or below 1.0 percent and CVCM at or below 0.10 percent).
- UL 94 – Standard for Tests for Flammability of Plastic Materials for Parts in Devices and Appliances (classes HB, V-2, V-1, V-0, 5V; grade- and thickness-specific).
- IEC 60243 – Electric strength of insulating materials (dielectric strength, kV/mm), for mica and film barriers.
- GB 38031 and the corresponding UN-type regulation – electric-vehicle battery thermal-runaway and propagation safety (assembly-level requirements owned by the pack maker), the basis for fire-barrier selection.
- Manufacturer technical data sheets for silica aerogel blanket (including cryogenic grades), polyimide foam (including aerospace grades), mica barrier sheet, and glass-fiber paper, the source of grade-level conductivity, temperature, flame class, dielectric strength, and outgassing figures. Confirm current grade designations and properties on the manufacturer’s current technical data sheet.
Related reading
This article cites general engineering principles and published test standards (ASTM C177 for insulation conductivity, ASTM E595 for vacuum outgassing, UL 94 for flammability, IEC 60243 for dielectric strength, and the GB 38031 and UN-type battery propagation-safety regulations at the assembly level). Material names refer to insulation and barrier families H-O Products converts, identified by material type.
Performance figures are grade dependent and illustrative; confirm all values against the manufacturer’s current material data sheet and an engineering drawing review before specifying.
H-O Products is a precision die-cut converter and does not produce raw blanket, foam, or sheet stock.