UPDATE!! The pattern link should work now. Here's the pattern in all it's glory INCLUDING pictures and the chart!
http://www.knittinghelp.com/patterns/free-knitting-patterns-heart-double-knit-hot-pad
Hob, Amy used worsed weight cotton for this tutorial. If you choose to use something else just don't use acrylic if you intend to use it as a hotpad.. acrylic can melt.

I think I'd go with wool myself for it's insulating properties.