FAR 25.856 Guide
What Is FAR 25.856? Aircraft Insulation Flammability & Burnthrough, Explained
The FAA's flammability rule for aircraft thermal/acoustic insulation — what paragraphs (a) and (b) mean, the radiant-panel and burnthrough tests behind them, and the insulation splicing tapes tested to 25.856(a).
FAR 25.856 (formally 14 CFR § 25.856, “Thermal/Acoustic insulation materials”) is the U.S. Federal Aviation Regulation that sets flammability requirements for the thermal and acoustic insulation installed in the fuselage of transport-category aircraft — the blankets behind the cabin sidewalls and crown, and the films, fasteners, and splicing tapes that go with them. It was added by Amendment 25-111 in 2003 and replaced the older Bunsen-burner approach for insulation with two tougher tests: a flame-propagation test and a burnthrough-resistance test. When an insulation splicing tape's data sheet says it “meets FAR 25.856(a),” it means the material passed the radiant-panel flame-propagation criteria in Part VI of Appendix F.
See every FAR 25.856-tested insulation tape we stock.
View FAR 25.856 Tapes →What the FAR 25.856 paragraphs mean
FAR 25.856 has two paragraphs, each pointing to a different test in Appendix F. A drawing or data sheet will usually cite the specific one. Here's how they break down:
Flame propagation — radiant panel test (Part VI, Appendix F). Applies to thermal/acoustic insulation installed anywhere in the fuselage. This is the criterion most insulation splicing tapes are tested to. It does not apply to “small parts.”
Burnthrough — flame penetration resistance (Part VII, Appendix F). Applies to insulation in the lower half of the fuselage on airplanes seating 20 or more, where a post-crash fuel fire would strike from below.
The radiant-panel apparatus used for the (a) flame-propagation test — it measures how far a flame spreads across the insulation and how long it keeps burning after the igniter is removed.
The oil-burner apparatus used for the (b) burnthrough test — it measures how long the insulation resists a high-intensity flame and limits the heat that passes through.
Related regulations. Cabin interior materials fall under FAR 25.853, and cargo-compartment liners under FAR 25.855. Aerospace tapes are often qualified to more than one of these at once — for example, our insulation splicing tapes reference both 25.853 and 25.856(a). See our FAR 25.853 guide for the cabin-interior side.
The two FAR 25.856 tests
The regulation replaced the single Bunsen-burner test with two separate fire tests, each targeting a different real-world fire scenario:
| Test | 25.856(a) — Flame propagation | 25.856(b) — Burnthrough |
|---|---|---|
| Appendix F part | Part VI (radiant panel) | Part VII (oil burner) |
| Fire scenario | In-flight / ramp ignition spreading across insulation | Post-crash external fuel fire penetrating the fuselage |
| What it measures | Flame spread distance & flame time after igniter removal | Time to burnthrough & back-side heat flux |
| Typical pass criteria | Limited flame propagation; self-extinguishing after the igniter is removed | Resist penetration for at least 4 minutes; back-side heat flux below 2.0 BTU/ft²·s |
| Where it applies | Insulation anywhere in the fuselage | Lower-half fuselage, airplanes seating 20+ |
How tape qualification works. A roll of splicing tape isn't “FAR 25.856 certified” on its own — the regulation governs the insulation system as installed. What a tape data sheet shows is that the tape has been tested to the 25.856(a) flame-propagation criteria as part of that system, with the typical values listed. Always confirm the tape is qualified for your specific blanket, film, and installation.
Insulation cover-splicing tapes for 25.856(a) work
Most buyers reach FAR 25.856 from an insulation-blanket job — splicing a cover film, sealing a seam, repairing a blanket. The E&H insulation splicing tapes below are all BMS 5-157 cover-splicing tapes in the same family; the metalized Tedlar 770-3FRD is explicitly tested to the 25.856(a) radiant-panel criteria, and the BMS 5-157 series is commonly qualified to 25.856(a) as part of the insulation system. Always confirm the exact 25.856(a) callout against each product's data sheet for your installation.
| Product | Film / application | 25.856(a) status |
|---|---|---|
| E&H 770-3FRD | Metalized Tedlar blanket splicing (DMS-1984; 25.853) | Explicitly tested — Radiant Heat Panel |
| E&H 753-MPE & 753-MP | Metalized PEEK cover splicing — highest grade (BMS 5-157; BSS-7230) | BMS 5-157 family — confirm on TDS |
| E&H 743-MT | Metalized PVF (Tedlar) cover splicing (BMS 5-157; GAT100FR1) | BMS 5-157 family — confirm on TDS |
| E&H 743-T | White PVF (Tedlar) cover splicing (BMS 5-157; GAT100FR2) | BMS 5-157 family — confirm on TDS |
| E&H 743-BLK | Black PVF cover splicing (BSS-7230; 25.853) | BMS 5-157 family — confirm on TDS |
Working from a Boeing insulation callout? Many 25.856(a) insulation tapes are specified through Boeing BMS 5-157. For decoding a Type / Class / Grade / Composition callout and matching it to the right E&H tape, see our BMS 5-157 guide.
Need the data sheets? Typical flame-propagation values for each product are on its technical data sheet. Browse them all in our Technical Data Sheets library, or see the full spec cross-reference on our Specifications by Authority page.
Frequently asked questions
What is FAR 25.856?
FAR 25.856 (14 CFR § 25.856) is the U.S. Federal Aviation Regulation governing the flammability of thermal and acoustic insulation materials installed in the fuselage of transport-category aircraft. Added by Amendment 25-111 in 2003, it defines two fire tests — a flame-propagation (radiant panel) test and a burnthrough (flame penetration) test — in Parts VI and VII of Appendix F.
What does FAR 25.856(a) require?
Paragraph (a) requires thermal/acoustic insulation installed in the fuselage to pass the flame-propagation test in Part VI of Appendix F — the radiant-panel test. The material's flame spread must stay limited and it must self-extinguish after the ignition source is removed. The requirement does not apply to “small parts.”
What is the difference between FAR 25.856(a) and 25.856(b)?
Paragraph (a) is the flame-propagation (radiant panel) test that applies to insulation anywhere in the fuselage. Paragraph (b) is the burnthrough (flame penetration) test that applies to insulation in the lower half of the fuselage on airplanes seating 20 or more, to resist a post-crash external fuel fire. Insulation splicing tapes are typically tested to (a).
What are the FAR 25.856(b) burnthrough pass criteria?
The burnthrough (oil-burner) test in Part VII of Appendix F generally requires the insulation system to resist flame penetration for at least 4 minutes and to keep the heat flux on the back side below about 2.0 BTU/ft²·s. It applies to lower-half fuselage insulation on airplanes with a passenger capacity of 20 or greater.
Is an insulation tape “FAR 25.856 certified”?
Not on its own. The regulation governs the insulation system as installed, not a single roll of tape. A tape data sheet shows the typical values from testing to the 25.856(a) flame-propagation criteria; always confirm qualification for your specific blanket, cover film, and installation.
What is the difference between FAR 25.853, 25.855, and 25.856?
25.853 covers cabin interior compartment flammability; 25.855 covers cargo and baggage compartment liners; and 25.856 covers thermal/acoustic insulation, including flame propagation and burnthrough resistance. Many aerospace tapes are qualified to more than one of these depending on where they are installed.
Not sure which 25.856-tested insulation tape you need?
Tell us the application, the spec or paragraph called out on your drawing (or the BMS 5-157 callout), and the quantity, and we'll confirm the right insulation splicing tape, stocked sizes, lead time, and pricing. Certificate of Conformance available on request.
Ask Our Team →This guide is provided for general reference and is drawn from 14 CFR § 25.856, Appendix F to Part 25 (Parts VI and VII), and the related FAA Advisory Circulars. Regulatory citations and test criteria may be amended; always verify current requirements against the controlling regulation, the FAA Aircraft Materials Fire Test Handbook, and your applicable drawing or material specification. Boeing, BMS, and BSS are trademarks of The Boeing Company; Gulfstream and GAT are trademarks of Gulfstream Aerospace; other marks belong to their respective owners. Typical product test values are stated at time of manufacture and are not for use in writing specifications. Insulation compliance must be established for the specific material and installation.