Is 400 Threads-per-inch fabric SOFT enough?

I am shopping (Amazon.com) for a cover for my foam wedge I use on my bed. I cannot sleep / wear any fabric made of polyester material. Comparing Cotton Wedge-shaped pillow covers, should a 400 thread-count (number of threads per inch) provide a Cooling-feel to my head when I sleep on it / even-though the 7 inch... show more I am shopping (Amazon.com) for a cover for my foam wedge I use on my bed.
I cannot sleep / wear any fabric made of polyester material. Comparing Cotton Wedge-shaped pillow covers, should a 400 thread-count (number of threads per inch) provide a Cooling-feel to my head when I sleep on it / even-though the 7 inch thick wedge is made of polyester foam material?
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