So, you're shopping for tees and you come across a page like this--lots of bullets, lots of %'s, and lots of "triblends!" or "100% cottons!"
Well, here's a quick primer: Ringspun cotton is yarn woven by twisting and thinning, ultimately to keep the short hairs out. This makes a soft, durable fabric, which means your 3650 may last longer than traditional cotton. Rayon is (usually) wood pulp turned into fiber. Polyester: synthetic fiber that keeps the water out (mostly) and lasts and lasts and lasts. Questions?