Good quality cover. Holds water well. No leaks. Probably stays cool if kept on cool surface, such as tile floor. Cotton cover probably cuts down on cooling factor a little, but makes for a much more attractive bed. Beware, however. If your dog likes to circle 'round several times before lying down to get rid of "lumps and bumps" this bed probably won't work for you. My German Shepherd ended up shifting the inner core contents into a lumpy mess in her attempts to smooth out this already smooth bed. As others have said, the larger sizes will be too heavy to move once filled with water so go with the smallest size that works for your dog. I'm not sorry I purchased it; just sorry it didn't work for my finicky dog.