When choosing Flame-Resistant insulated outerwear it would be good to know how well it works at keeping you warm. That can be very important when working in extremely cold environments. Test methods have been developed for estimating temperature ratings for insulated garments. The new ANSI/ISEA 201 Standard for Classification of Insulating Apparel Used in Cold Work Environments defines temperature rating as “The coldest environment temperature at which a person can remain thermally neutral while wearing a particular clothing ensemble (neither gaining nor losing heat to the environment) at a specified activity level or metabolic rate.” The temperature rating is reported as a temperature of the environment at a particular work activity level specified in Metabolic Equivalent of Task (MET). For example; 32° F (0° C) for light work activity (2 MET), -15° F (-26° C) for moderate to heavy work activity (4 MET). The Institute for Environmental Research lab at Kansas State University has a testing facility to perform full body manikin testing to estimate the temperature ratings for garments. By having such a rating, wearers can now know the low temperature at which a garment will provide sufficient warmth.

What exactly is MET?
MET stands for “Metabolic Equivalent of Task”. ANSI/ISEA 201 defines 1 MET as “the amount of heat produced by a man at rest (1 MET = 58 W/m².) Metabolic heat production is directly affected by a person’s activity level. A person’s activity level can vary. A person who is walking slowly produces about 2 MET of heat, whereas, a person who is walking very fast produces about 4 MET. As a person’s activity level increases, the amount of metabolic heat produced by the body increases, and less insulation is needed for comfort.

What is Clo Value?
Another term commonly used when speaking about cold weather garments is clo value. Clo is a measure of thermal insulation capability, for apparel insulation (similar to R-value for home insulation). The higher the clo, the warmer the person will be. The colder the environment, the greater amount of clo, or clothing insulation, will be required to be comfortable at the same activity level. The definition of clo is: 1 clo is the amount of thermal insulation required, for clothing, to be comfortable in a normally ventilated room at 70° F (21° C) and

How to Determine a Temperature Rating?
The temperature rating of a garment or garment ensemble is determined by testing them using ASTM F2732 Standard Practice for Determining the Temperature Rating for Cold Weather Protective Clothing. A typical rating for a jacket is done by placing it on an instrumented manikin dressed in a standardized clothing ensemble of a 6.3 oz knit mock turtleneck shirt, 11.7 oz jeans, knit hat, insulated knit gloves, socks and athletic shoes. The test method measures the heat loss and calculates the temperature rating based on the manikin remaining thermally neutral. This method can be used for all insulated garments whether they are FR or not. Adding additional layers of clothing such as an insulated bib overall will dramatically affect the numbers since the lower part of the body will now be insulated as well – not just the areas under the jacket. The temperature rating/prediction is a guideline since the manikin is a steady-state model, the calculations assume even distribution of the ensemble, and real world conditions change throughout the day.

Summary:
The ratings for garments are specific to the combination of materials (outer shell, insulation material, inner lining) and garment configuration used in the testing. It is not practical to test every combination and configuration. However, the relative rating for those specific insulated garments provides a guideline on which to make a decision.

Examples of possible test results:

Style X Jacket Only

Style X Jacket & Bib

Style Y Jacket & Bib

Rating @ MET 2

47.3° F

29.9° F

34.4° F

Rating @ MET 4

-0.3° F

-35.8° F

-26.6° F