As a couple of sweaty walruses, we are always worried about being too hot & waking up, or our sheets moving (or just not working) and getting the mattress all sweaty and gross. This cover fits and doesn’t shift around. It’s just as comfortable as the mattress has been all along. We’re debating if it’s kept us cooler or if it was just the weather we’ve had, but it certainly didn’t make things hotter, which we really appreciate.