Do waterproof mattress protectors make the bed hot?

This is the single most common complaint across r/Mattress and r/Bedding threads. Reviewers consistently report that cheaper polyurethane-backed protectors trap heat, while bamboo, Tencel/lyocell, and cotton-terry tops breathe noticeably better. Hot sleepers should prioritize a Tencel or bamboo top layer over a plain polyester quilt.