Where does my Mattress Protector go? August 11, 2020 20:08 The Helix Mattress Protector fits snugly around your mattress, under your fitted sheet. Related articles Will the mattress protector make me sleep hotter? Can I buy the Mattress Protector without buying a Helix Mattress? What does the Mattress Protector do? Can I wash my Ultra-Cool Pad? Does the Weighted Blanket get hot?