Polyester, how wonderful. Any benefit this provides is cancelled by using polyester instead of some good breathable material. I think I'd rather use a "dumb" wool cover.
If you look at the tech specs section on http://lunasleep.com you'll notice from the drawings that a mattress pad is composed of multiple layers, if we use natural fibers for all the layers, say for the filling (batting), the product would never dry and could grow mold (that's why ALL the heating pads on the market and most mattress pads are made of polyester).
One thing we could do is think about a premium version with the top layer (and maybe the bottom layer?) made of 100% cotton. Such a product would cost a little more (about $30) and take a little longer to dry completely after washing.
Would you guys be interested in such a premium product?
EDIT: formatting