I use every part of the sweaters I craft with, even the dryer lint! I have been saving the wool dryer lint to put in a suet holder for the birds to make nests with in the spring (i've seen that in a few places online, so I don't know who to give the credit too for that brilliant idea!). I can't think of a better material to use... wool is insulating, biodegradable, and natural. Since I use all natural detergents that rinse out well, and wool dryer balls, there are no chemicals in my lint either.
Now for the part where you either "awww" or "ewww"... depending on whether you view mice as cuties or vermin. My son's mouse, Jackhammer, has developed allergies to something & has been scratching herself until she bleeds. I have been trying to figure out what she's allergic to, and she's on meds to try to stop the itching (yes. I took her to the vet). This morning I remembered that wool is hypoallergetic, and put in a handful of wool dryer lint. Jackhammer immediately made herself a nest with it, and I don't see her scratching while she's in it. I'm sure it could be coincidence, but hopefully this will help the poor thing. I couldn't get a non-blurry picture of her... didn't want to use the flash & freak her out, and she wouldn't stop wiggling her nose, but isn't she cute? :)
Bottom line? Clean wool lint/tiny scraps makes a great & natural nesting material for small pets!