Taken from Warbonnets web page on the spinddrift.
The Spindrift is our sock for the Ridgerunner, a "sock" (named after a tubular windsock) is a giant fabric sack that the hammock hangs entirely inside of. They're made of fabric that is both wind and water resistant but is breathable enough so you can keep it zipped up. The entire hammock (including your underquilt) hangs inside the sock, creating an enclosed protected space. Since the space is enclosed, you'll usually notice an increase of 15-20deg or more compared to the outside air temp, this can help alot when the temperature approaches the limit of your top or underquilt. Socks are normally used in colder weather. If conditions contain rain or heavy wet snow you'll want a tarp in addition to the sock as the sock is water-resistant, not waterproof.
DWR finish is water resistant,,not waterproof which is the same for Momentum 90 MR. BlackWolf,,if your going to the artic..what do the artic explorers use,,when they are pitching tents? However,,I am asuming,,your going to try and hammock off the ground in a artic atmosphere,,so your going to be seeking something that is windproof, waterproof, and yet, has to have somewhat breathable ablitities to keep from icing on the inside.??? Just guessing.
But with a tarp over the Spindrift when enclosed ends, and as close to the ground or snow packed on the sides, breaking wind, and creating yet another micro climate of sorts, hence micro climate inside a micro climate with the hammock in the middle. Canvas can get wet, can get iced, brittle, and even if some water resistance,,eventually soaks all the way thru. I had for years, a canvas pullover with hood,,that I used for Tuna, and shark fishing, off the coast of Connecticut...out on the grand banks,,and it was great to a point. It couldn't beat the gortex, or other space age materials we have available to us today.