It is a comfortable room temperature inside the caves and not cold at all, so you don't need to bring extra sweaters or jackets. (brittanymthiessen.com)
I have 3 outfits in each, a couple extra sweaters for variety, and a few workout clothes. (truncationblog.com)
Uniqlo's Heattech line has been a big hit with people for whom an extra sweater just isn't enough, while Columbia Sportswear has developed reflective heat tech to keep winter clothing warm. (fortune.com)