I have never tried it on towels. I have done cross stitch designs on sweatshirts. They sewed out beautifully. You certainly would need at least 1 layer of WSS on each side, possibly more. Try it on an old towel and let us know how it comes out. I also think it needs to be a tight stitch to help keep the loops from coming up.

I added a picture of a handtowel that was embroidered in crossstitch and I did it just all my other towels.

Goodluck