High on the Mountain Top
Join Date: Apr 2010
Location: Burnaby, BC, Canada.
Comparing in the store, I didn't notice significant packing size differences between the MEC Scout Tarps.
The silnylon one is a bit lighter, but I selected it over the poly one primarily because it's 'cleaner', i.e., with its slippery surface, it's very easy to wipe off dirt, mud, leaves and branches when packing it away.
But it's less waterproof - you do need to pitch it tight (and re-tighten every so often) at a steeper pitch with no flat spots, to ensure water rolls off and not seep through. It's not good for ground sheets or wrapping packs or equipment to keep things dry.