The two images above are on 24" x 33" commercial printing paper. My guess is that it's 100# cover weight or slightly heavier. Not sure really since it was a gift from my neighbor who found it while dumpster diving. It's surface is slippery and nearly non-absorbent so I textured it by painting on a layer of primer shellac containing pumice. That helped some with the slippery but it made it totally non-absorbent.
Three above are on 36" x 24" newsprint paper. Ink, acrylic, chalks.