Ensuring optimal thermal performance

Footwear which is intended to be worn in a cold environment needs to be fit for purpose. How can such a characteristic can be accurately assessed?

by Tom Bayes

The ability of footwear to provide protection against the cold is an important one. Normally, this is strongly associated with foot comfort in cold conditions, but it is important to consider that a lack of adequate performance can lead to foot health problems and even legal action in an occupational setting.

EN ISO 20345 and associated standards allow for the testing of cold environment footwear with a relatively simple evaluation. Unfortunately, it does not discriminate sufficiently to allow footwear to be selected for different cold environments, such as a chilled room as opposed to a walk-in freezer. This can lead to discomfort, dissatisfaction and potential issues if the footwear is not ‘up to the challenge’. For this reason, many specifications are now calling on the SATRA TM436:2010 – ‘Determination of whole shoe thermal insulation value and cold rating’ test method to provide a more in-depth assessment of the footwear’s suitability to withstand cold environments.

SATRA TM436 allows the whole footwear insulation value to be measured in a precise and repeatable manner. The result is the ‘R’ value for the footwear, the ‘R’ value being the SI unit for insulation properties of individual materials or combinations of materials. However, SATRA TM436 goes much further than simply providing a measure of the insulation properties. It uses the ‘R’ value, along with desired heat flows and other parameters, to predict and forecast a temperature where foot comfort can be achieved. In addition, the method allows for the activity level of the wearer – whether sedentary or very active – to be taken into account, and this makes a difference to the amount of insulation required.

Too much can become a bad thing

Although sounding contradictory, too much insulation can be undesirable for cold-weather footwear, as the product becomes more bulky and, if it is too well insulated, this can promote perspiration of the feet. In this situation, moisture will build up in the footwear, which can lead to discomfort. The presence of moisture will also negatively impact the thermal performance, thus reducing the effectiveness of the insulation. This occurs especially if the activity rate is high, such as in heavy manual labour. A balance is required to produce the correct level of thermal comfort for the wearer.

SATRA TM436 allows for the ranking of footwear and, if given a target temperature, it is possible to rate footwear as both ‘warmer’ and ‘cooler’ either side of the target temperature, thus allowing for individual preference.

An evaluation is conducted on the SATRA STM 567 ‘Endofoot’ machine. The test is simply set up and left to run, with all timing, measurement and cold temperature calculation being handled by the associated software. Three consecutive measurements are made and the final result is calculated and presented to the technician without the requirement of any further manual intervention.

In combination with STM 567, SATRA TM436 is the ‘go-to’ thermal performance assessment for footwear, and is rapidly being adopted in specifications across the industry. It is able to provide accurate consumer information, allowing footwear to be specifically selected or designed for particular cold environment situations.

Publishing Data

This article was originally published on page 36 of the November 2021 issue of SATRA Bulletin.

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