If you need a pillowcase or cover for your cooling pillow, then a 100% cotton or bamboo rayon cover would be best. Also, check that the thread count is not too high. You want less than 400 TC because the lower the thread count, the looser the fabric and therefore the more ventilation can pass through it. However, you will find that many cooling pillows come with a removable zippered cover. If so, it’s best not to use another pillowcase over that since you will lose much of the breathing capacity.