I made this material in the picture out of dryer lint and Elmer's white glue.
To make it take the dryer lint and tear it into as small pieces as you can and keep mixing it together until it is as uniform as you can get it, also remove any pieces of any sort of non dryer lint particles that might be in there. Then gradually mix in the glue (I used Elmer's but I might even try some kind of epoxy next time). Knead it like dough, it will absorb a ton of glue, like maybe half of a good size bottle. I'm not sure on the exact amount I kind of had to guess. Then set it out in the sun for about a week, for the first few days it will feel like it gives when you press it, but forms a hard crust on the outside, eventually it will dry all the way through and be hard as a board and not give at all no matter how hard you press.
I had the idea based on how they make carbon fiber but this uses cotton fiber that's been processed in the dryer, which I think everyone throws away anyway. I think the real useful property of this material is that because it's made out of cotton fiber it won't conduct heat! Like imagine an inch think solid sweater how warm that would be. So my first thought would be as a possible replacement for drywall, that is stronger and doesn't conduct heat to better insulate a house. But also it could be fun to make sculptures or anything else out of it.
A couple more things, I think it would be fun and safe for kids to use (when you are kneading it is really gushy I think they would like that), and I noticed that it is naturally buoyant, the sample in the picture floats half out of a glass of water longways. I believe that it would also be pretty soundproof, but they would probably have to mix in a flame retardant before they use it in structures.