but I could be mistaken. Anyway, I know exactly what you're referring to. Home Depot sold it in rolls as bulk furnace filter material. It is a blue open-weave poly material of some sort. I bought a roll several years ago to put under our mattresses which were developing horrible condensation underneath. This stuff provided just a bit of air space and has worked wonderfully for the past ten years.
Oh yeah, it's cheap.
I'm not positive but I did a quick search and I think this is the stuff you're looking for.