The simple answer to this is the number of walls. 2 vs 1. But what does it imply?

It’s not just that 2 walls keep you warmer than 1 wall in cold weather, double wall tents are known to keep you dry even better than single wall tents. This is because in a double wall tent, the fly keeps the rain and snow at bay while the inner tent expels the moist air so that it condenses on the fly (in cases ventilation doesn’t do the trick) which then drips to the ground instead of the user.

A single wall tent has to rely on one wall to do both i.e. deal with moisture from inside and outside. So the fabric has to be waterproof and breathable. Breathable fabrics may not be enough to battle condensation effectively so you have to rely on venting.

The upside to single wall tents is that they’re lighter and less bulky. Double wall tents have more parts and hence heavier and bulkier.

Outdoor Research: How to Setup A Bivy Sack from Outdoor Research on Vimeo.

“Bivy sacks are great solo lightweight shelters which can also be carried as a backup emergency shelter. Today we are going to talk about Outdoor Research’s Advanced bivy, which includes 2 poles. It’s a two pole system designed to keep the bivy material off your face.

As you’re thinking about setting up your bivy, first off, you would want to choose an appropriate site. Make sure the area is clear of sharp rocks or other debris that might puncture the fabric of the bivy sack.

Once you’ve done so, go ahead the pull the sack out of its pack and set up its poles. So you’ve got two different poles, one longer than the other. The longer pole is going to go on the inside of the white sleeve. Connect the end pieces at both ends and connect them to the corresponding snaps.

The shorter pole goes into the grey sleeve on the outside. Connect the end pieces at both ends and snap them into place. The sack is now ready.”

There are two straps inside the sack that you can use to strap in your camping mattress. The one used in the video is probably an Exped DownMat 9 by Outdoor Research.

There a variety of configurations you can choose from. The video shows all the possible combinations.