What do the 'seasons' ratings mean?
Giving definitive temperature ratings for sleeping bags is a notoriously tricky business. Season ratings are a good starting point for people in the UK as many people have an idea of the times of year that they will be sleeping outdoors. Seasonal ratings are quoted for bags being used at sea level, generally air temperature drops with increased altitude by about 1°C for every 150 vertical metres (this can vary). So if you're intending to sleep up high keep this in mind. The seasonal rating system we use is related to minimum expected temperature. They are not absolute but we believe they correlate to most people's ideas of seasonal UK temperatures.
Suitable for use in summer only (lower limit of +5°C or higher)
Suitable for use from late spring to early autumn (lower limit of between +5°C and 0°C)
Suitable for use through spring, summer and autumn (lower limit of between 0°C and -5°C)
Suitable for use all year round but generally in winter conditions, too warm for summer conditions (lower limit of below -5°C)
As well as having a lower limit of below -5°C expedition bags will typically feature very high quality down in order to reduce bulk and weight, water-resistant outer shells and extra length and width to accommodate bulky clothing and to allow you to dry clothing items inside overnight.