I've got the SDK smalls and they don't hold as much as the simple mediums as you would expect (smaller = less padding) I've had but they fit snug, if not, perfect for me. They feel really nice when wet though since it's more snug. I drunk about 2 liters one afternoon and found myself soaking it 3 times with only slight leakage and a little pooling on the 2nd and 3rd one waiting for it to absorb. So in all I give it 2 thumbs up.