Snip off a scrap, hold with tweezers and burn that lil sucker. If it melts back onto itself, even a bit, its a poly blend. If it just goes black, brittle and ashy it's cotton. If its a poly blend it will never soften. If its cotton, there's hope. Did it shrink at all when you washed it? Soak in vinegar overnight then wash in hot water. If that doesn't work, its been over treated with sizing and no good. The only way then for a softer outcome is to use a few layers of flannel and chenille cut it.