I'm not a textile engineer, so you can't hold me to this, but to my knowledge, rayon is actually a natural material made by processing some sort of plant fiber. I used to think it was a synthetic too. I think a lot of people make this mistake because rayon feels very different from wool and cotton, as rather more similar to some forms of polyester. BTW, and I AM a chemical engineer, so do take my word for it, polyester is not a specific material, just the name for a whole family of materials made distinguished by repeating ester functional groups joining long, chain like carbon and hydrogen structures. I generally like my suits to be 100% wool and my dress shirts 100% cotton, but I would be hesitant about condemning a whole class of materials. Shirts with some fraction of polyamide and elastane, for example, tend to keep their shape better than many cotton weaves, and many designers use these rather expensive materials to rather good effect. There are good quality synthetics and bad quality synthetics, just like there is a range of qualities of wool and cotton. And a judicious addition of synthetics may make an otherwise mediocre wool suit feel nearly as springy as if it were a 100% wool suit costs double the price (I suspect that this is why there are many suits out there with 1% elastane).