Are zippered encasements hot to sleep on?

This is the most consistent complaint across reviewer communities. Waterproof TPU/polyurethane-backed encasements trap heat and can feel clammy; r/Mattress threads repeatedly describe sleeping on "the blob." Cotton-faced or jersey-knit encasements breathe noticeably better but may sacrifice some waterproofing. Pairing any encasement with a breathable mattress pad on top is a common workaround.