There is a somewhat lower temperature rating on the Mountain Equipment Xero 550 compared to some other bags, with it being comfortable for the average man down to -8 degrees C. It is a good size of 213cm long and 79cm shoulder width, but that results in it being somewhat heavier at 1041g compared to some bags and it doesn’t include a stuffsack. Inside there is high-quality insulation that is comprised of 93 per cent down and only 7 per cent feather. The down is sourced ethically and the Mountain Equipment Down Codex programme audits its production.


The outer fabric, for maximum efficiency, contains stretch fibres which results in the bag hugging the body a bit closer in order to prevent there being any cold spots. Slant wall baffles capture the down to also help minimise cold spots. The bag’s side zip does not extend all the way to the foot, but stops near the calf area instead. I like that since it enables my feet to remain cosy while venting my legs. Behind the zip there is great baffle along with an anti-snag strip. Those work together together well without the zip becoming jammed. It comes with a well-profiled hood and large shoulder baffle, and the shoulder and hood drawcords both work quite smoothly. There isn’t any additional water resistance to the shell or down, though, so it is very important for the Mountain Equipment Zero 500 to be protected from any tent condensation. The stuffsack also doesn’t have a way to compress down into pack size.


The Mountain Equipment Xero 550 is an excellent year-round bag that comes with a great assortment of well-designed features; however, it is lacking in certain benefits including a compression stuffsack and better water resistance.