As you can see, it packs way down but can expand. I don’t know whether it insulates better when it opens up than when it is mashed flat. I don’t think the guys let it expand very much.
I was told that the materials were developed to insulate space capsules, then adapted for buildings. So the black plastic layer is quite stiff and tough. The layers of foil are no thicker than the stuff you cook with but are much stronger. The wooly stuff in between might be wool, I don’t know. I know the guys like working with this because it is not fiberglass. They don’t have to worry about what they are breathing and their skin doesn’t itch.
These photos are not protected in any way. You can probably download them if you like, to take to your favorite building supply store.
The stuff wasn’t cheap. I can’t quote a price because I didn’t buy it myself but my contractor kept saying it cost a bundle. However I believe it to be well worth the money. It insulates extremely well. I don’t have to worry about the guys getting some horrible disease from breathing fiberglass. It packs down thin enough that we were able to retain the original cove moldings, with just the tiniest trim piece to disguise the new wall. As with most of the money that went into this house, now that it is done, you would never know.