"This may not come out of your gear closet often."
It is a mat cover, so it covers the mat. I got this specifically for backpacking when I'm just going to sleep on the ground under the stars. Or to use with a bivy, but under the bivy instead of inside it, cuz I squirm a lot and it's more comfortable that way. The cover works well for both of these uses in keeping the mat protected, dry and free of dirt (only the bottom is waterproof I think). But honesty, Exped mats are so tough to begin with that it's not really needed. I would probably skip this unless you like to collect gear. I still give it five stars cuz it is quality and does what it's supposed to.