Hi Sckendrick,
You can see a picture of it here which I believe is current (although the lighting makes it look darker than it apparently is). It’s a good quality stretch knit and of course is less costly than a wool quilted cotton cover (which SleepEz also provides on their other mattresses). If you call them they can give you any more specific information that you may need.
You can also read more about the tradeoffs between a stretch knit cover and a wool quilted cover in post #6 here.
Phoenix