The Birch, Birch Lux and Birch Supreme offer three insulation weights in an Outwell mummy profile, chosen to balance comfort with performance.
Length and width are larger than the norm for such sleeping bags to allow freedom of movement and the classic mummy shape ensures a cosy fit to help retain heat. Flexibility is assured by a generous hood plus shoulder and zip baffles.
Outwell uses its time proven Isofill polyester insulation to ensure efficient heat retention and has carefully chosen fabrics that provide next to skin comfort.
Temperature control is easily regulated on a warm night by the two-way L-shaped side zip that can be opened to allow feet to cool or fully unzipped to create a duvet. The easy glide zip ensures trouble free operation.
All Birch sleeping bags feature a convenient removable pillow and a cap compression sack.
Temperature and season ratings
To determine temperature limits of the sleeping bags objectively, the European Standard EN ISO 23537-1:2016 on requirements for sleeping bags specifies the use of a computer-controlled thermal manikin similar in shape and size to the human body.
A sleeping bag containing a manikin is placed inside a temperature-controlled climate chamber and tested in accordance with a prescribed procedure to determine the thermal insulation properties of the bag.
Recommended temperature limits are based on the insulation properties measured and on knowledge of how the human body reacts to thermal conditions during sleep. (All double bags are tested with one manikin only and therefore the temperatures are most likely to be different from the one stated if two people are using the bags).