Loaded with innovation, the Therm-A-Rest Saros is a bag with a great deal of potential.

The shape is classic mummy with nice internal volume around the shoulders and torso. The underside is uninsulated, instead relying on your sleeping mat to take care of conductive heat loss. Using the connector loops on the back of the bag makes for simple and effective mattress attachment. This configuration reduces to zero the risk of being separated from your mat while you sleep – regardless of your thrashings.

The fill is eraLoft, a synthetic hollow core microfibre designed to trap then harness the warm air inside the bag. Working in conjunction with the bag’s differential cut (construction providing consistent fill volume around the bag), zoned insulation to keep fill where it should be, and the DWR-coated 20D polyester soft-touch fabrics, the bag stays comfortable all night long.

The stash pocket is mounted externally and close to the shoulder, yet is surprisingly unobtrusive. Because the bag is attached to its mat, even with a headlight inside the pocket it can’t be felt as you move. Reaching out through the hood opening to get it during a cold night can be a little tedious when your arms are warm inside.

However, there are problems at both ends of the Saros. The hood’s adjustment cord is super-thin, and although I tried to manipulate the opening with it, the hood’s top edge rested squarely across the bridge of my nose. And the not-so-comfortable foot box tips your feet inward, made worse if you want to spread them apart.  

By using light materials, and with no underside insulation, Therm-A-Rest has endeavoured to keep the Saros’ weight down, but at 1345g it’s not the lightest choice. However, taking these into account, and the great price, the Saros is beautifully finished and sports some excellent all-round features.