Are the t-shirts wearable? If so, why not donate them to Goodwill/Salvation Army/etc. If not wearable, how about cutting them up and using them for stuffing dog beds? What about taking your favorites and making a t-shirt quilt? I've also seen on Pinterest "upcycling" t-shirts - cutting them/slashing them to make scarves, new t-shirts, etc. Just some thoughts...
I've never seen anything about using t-shirt weight material instead of batting. I believe it would be too thin, so it wouldn't work as batting. I'm interested in what other QB members have to say on this.
Anita