For heat what? You live somewhere hot, you want to retain heat, you are worried it will retain heat?

I think that fiber content is more important. Were you considering cotton, rayon, silk, or what?

For our couch set, we chose a microfiber fabric; it is comfortable in all seasons; I live in NJ and we have 30 degrees in winter and high 80’s in the summer. It is also stain resistant. It is very confortable to sit on too