I really wanted to love these, but they simply don't stay on the pillows, regardless of whether it's a standard or a king. They twist around the pillow and won't stay put at the edges. We tried different pillows in different sizes, but ultimately nothing changed. Also, the sleeve was not cooling in any way, and my hair kept coming loose from my bun and getting caught under the edge of the sleeve. I tried a few methods for tying up my hair, but the result was the same. The sleeve twisted around the pillow, and my hair came free.
I think this is a nice product for people who aren't looking to correct a problem (e.g. night sweats, insomnia, skin/hair issuess), but simply want to enhance what is already good sleep. If that's you, please buy them as they are very nice, but do be aware that the sleeve twists and does not stay put.
I just ordered a set of silk pillowcase covers with zippers for $50. Perhaps they'll work better. Bummer I spent over a hundred on these!