There is a standardised test for measuring thermal insulation of clothing called ASTM F1291-16. It is a laboratory test in a controlled environment using a heated mannequin. This allows you to compare the properties between different garments but is next to useless for providing a temperature rating for consumers as their are so many variables to take in to account when outside - temperature, change in temperature,  humidity, wind chill factor, fitness, metabolic rate, underlying health conditions, other layers of clothing, work rate.........As you can see, it would be impossible to provide a temperature rating when thermal comfort is so subjective and goverened by so many variables.. If you would like help selecting the right garments for your activity or would just like some advice then please contact our technical department on +44 (0)116 2402634 or sales@subzero.co.uk