This is a quality down comforter cover that is soft, thick, and definitely seems to be adequate for keeping out dust mites, pet dander, dead skin cells, and the like. It adds a considerable amount of weight to my 100% down comforter, but it is much easier to wash regularly than having my down comforter professionally cleaned; so I appreciate this encasement for that purpose.
However, what I am not happy with is the size of this cover. It is substantially smaller than my King-sized down comforter, therefore, my duvet covers are all lacking in substance by about 5 inches on each side, as well as from top to bottom. I have a lot of duvets and they are all much bigger than my comforter when using this cotton encasing, which is a bit of a bummer. Most of them have ties on each of the 4 corners, but even when tying up the comforter with this encasing on it, the sides of my duvet covers have an extra 5" or so of loose, unfilled fabric after making the bed... which is pretty disappointing. So now I am torn between having an allergy-free comforter that is too small for my duvets, or a bare comforter that fits the duvets perfectly. And given the heavy weight this adds to my down comforter, I imagine that this cover will only be good to use in the wintertime as it is much too heavy for use in the summer. So at this point, I think it was pretty much a wasted purchase as I expect after washing that it is going to shrink even more. If you are planning to use this cover as a duvet, then it will probably work well for you (although expect that it will shorten your duvet cover by a few inches around); but if you are planning to use it over your comforter and under a duvet, expect that none of your average king sized duvets are going to work well with it.