Aviation Stack Exchange is a question and answer site for aircraft pilots, mechanics, and enthusiasts. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I've seen some green "bags" on the SSJ100 when they were building it. What is the purpose of these?


share|improve this question
Looks like it's probably sound proofing/insulation/fire barrier material. – Ron Beyer Feb 11 at 17:28
Text attached to this image in the original article: "The fuselage of the aircraft from the inside is lined with green mats for thermal and acoustic insulation Photo: Alexey Petrov" – mins Feb 11 at 19:40
up vote 14 down vote accepted

That's cabin insulation - probably fiberglass.

It's not always in green bags (blankets), and not always fiberglass, but some kind of insulation is necessary to help control temperature and reduce cabin noise (air moving over the fuselage is REALLY loud).

Here are some other photos of different types of insulation:

Basic fiberglass with a plastic backing, cut to fit.
Fiberglass with either plastic or foil backings is commonly used because it is both light and inherently flame-retardant (as long as the backing is fireproof it will not burn).

Soundex Soundex composition
Soundex - a sandiwch of acoustic foam, thermal insulating foam and aluminum foil - is a popular choice on propeller aircraft: Slightly heaver than fiberglass, but better at dampening sound.

Foam padding
Foam padding (similar to the foam used under carpets) does a decent job at both sound and thermal insulation. In this case it's green & has no covering, but colors and coverings vary.

777 insulation blankets
Prefabricated insulation blankets on a Boeing 777.
(I believe these are fiberglass sealed in polyethylene, they're manufactured to fit each bay without cutting which avoids loose insulation material floating around).

share|improve this answer
And do they act as fire insulators also? – kepler22b Feb 11 at 19:41
Is there ever a chance to hear the REALLY LOUD air over fuselage sound? – curious_cat Feb 11 at 19:50
@curious_cat In a glider, sure. Much of the ambient white noise you hear on jets is also from wind noise (as opposed to engine noise). In propeller-driven planes the propeller noise typically dwarfs the wind noise. – voretaq7 Feb 11 at 20:12
@kepler22b While the insulation material is not flammable (by regulation) I would not expect it to be a particularly effective fire stop: It will delay heat propagation for a time, but its primary purpose is to reduce noise and keep the cabin warm and relatively quiet. (The FAA has done some studies on what happens when you try to burn aircraft insulation under conditions that might be found in an accident, the reports make for interesting, if technically dense, reading) – voretaq7 Feb 11 at 20:25
@voretaq7 But are gliders relatively quiet you would say or not at all? I've never been on one sadly. For example, on a scale of 1 to 100 (noisiest) if you had to rate a glider vs 747 vs prop plane how would they rate? – curious_cat Feb 12 at 3:21

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.