I haven't yet had time to poke around at Pixels.com to see if there is a way I can add a more helpful description of their merchandise bearing my designs. As far as I know, Pixels.com doesn't provide this information on its own.
Having ordered Pixels.com tote bags of my own, I can say this:
The tote bag is made from sturdy polyester. The fabric exterior is bonded with a layer of flexible plastic on the inside of the tote. I suspect the inside is waterproof because it looks that way, but I haven't tested this to see.
I've also ordered a T-shirt from Pixels.com and found the material to be of good quality -- not that cheap flimsy stuff that you sometimes find in some souvenoir shops.