Fill power is a measure of lofting and is based on the volume a measured weight of down will fill. The Lorch method is the current standard for testing loft in Europe and is the recommended standard of the International Down and Feather Laboratory. A 30g sample of down is placed in a clear tube and a 94.25g weight is placed over the down. The height the down maintains give its fill power and can be expressed as height in mm or volume in cubic inches. 

The greater the fill power, the greater the warmth for a given weight of down. For Terra Nova Laser bags we use a 900 fill power down, meaning that 30g of that down occupies 900 cubic inches. A larger quantity of down, or the use of an alternative will provide different figures, so it is important to bare this in mind when comparing different products. 

Our down is some of the best available and consists of pure white goose down mixed in a 95/5% split (95% down 5% feather). The higher the proportion of down, the better the quality. 

Our sleeping bags have been tested in accordance with BS EN 13537, which is the British and European standard for sleeping bags. The standard requires four temperature results to be displayed, which are as follows: 

Upper Limit is the temperature up to which a partially clad standard man can have a comfortable nights sleep without sweating. 

Comfort Rating is the lower limit at which a standard woman can have a comfortable nights sleep. 

Lower Limit is the lowest temperature at which a standard man can have a comfortable nights sleep. 

Extreme Rating is a survival rating for a standard woman. There is a risk of hypothermia and this temperature should not be approached. 

Sensitivity to temperature varies between individuals and depends on a number of physiological and environmental factors, all of which will influence a persons choice of sleeping bag.