the trouble with polyester is -- it can be so many things-- back in the 60's there was a form of polyester called "whipped cream"-- it was extreme soft and fine and breathable-- it went away and was replacece with poly double knits-- which-- again where fine for some things-- as IP, mentions, they are warm, and made good winter gear--

Micro fibers-- which are all the rage are similar to the old fashioned "whipped cream" ployester.

rayon is cool, and lightweight-- but it shrinks like cotton, and really doesn't want to be washed, but dry cleaned, wrinkles as bad or worse than linen...

One of my favorite summer fabics-- which cost a kings ransom, is very, very fine tropical weight wool. I has 100% wool dresses-- so light weight they were almost sheer! wool wicks away moisture, doesn't wrinkle, can be hand washed, it hold dyes well, so you have great colors and no color rub off-- (rayon, like cotton bleeds! i had having navy blue under arm pits!-- or other areas where fabric comes close to moist parts of your body) . But its very hard to find-- and when you do, you are looking at a $40 a yard fabric!