I gotta admit, I never even thought about putting a "sheet" inside of a sleeping bag until I heard about this product. But when you think about it, it makes sense. Would you want your blankets and the mattress immediately against you at night? Heck of a lot more difficult to wash than a set of sheets. Same principle. This item fits pretty well inside the TNH bag, not quite like a glove, but that just indicates that it would fit in almost any sleeping bag. Seems to be made rather well, but until I can run it through the laundry a few times I can't really say how it holds up.