Like the similar Rab Genesis 2, this is really a three-season rather than a summer only bag and should be adequate for warm sleepers in temperatures a degree or two below freezing. The thick insulation, double layered to cut out sewnthrough seams, is made from two types of fibre plus a thin fl eece layer with embedded metallic particles that are meant to speed up warm-up time and reflect back some body heat. I’ve only used the bag in above freezing temperatures when I’ve found it very warm – whether the metallic particles made any diff erence I can’t tell. The bag is well designed with a close-fitting hood, thick shoulder and zip baffles. The zip runs without snagging. The lining fabric feels warm and comfortable against the skin. The bag is quite narrow compared with some others and I could only comfortably wear base layers and a thin fleece inside. The weight and bulk are high though and this bag is better for car camping than backpacking. The Ultralite with the same design would probably be better for summer backpacking as it only weighs 950 grams.