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The ISO 11092 standard, Textile – Physiological – Measurements of Thermal and Water-Vapour Resistance Under Steady-State Conditions, can be used to evaluate a moisture barrier’s breathable performance both before and after heat exposure. Individual components or the entire ensemble can be tested for water vapor resistance, which is one method to measure breathability. This breathability is determined by measuring the amount of water vapor that can pass through a material in a given amount of time. The more easily the vapor can pass through a material, the more breathable it is. Therefore, a moisture barrier with a low resistance allows the perspiration vapor from your body to escape more easily.
Test results that show an increase in water vapor resistance after heat exposure indicate that the moisture barrier may have been affected by the heat. As shown in Figure 2, moisture barrier A maintained a consistent level of breathability, with resistance of approximately 5 m2Pa/W before and after exposure. Moisture barrier B, however, became significantly less breathable after heat exposure, with resistance increasing from approximately 8 m2Pa/W before to 17 m2Pa/W after heat exposure.
Durable performance of your gear
When you or your department purchases new turnout gear, it is important to consider the thermal stability of the individual layers (outer shell, thermal liner and moisture barrier). Keep in mind that performance of new gear may differ from its performance after it has been exposed to various levels of heat – especially if the components themselves are less thermally stable.
Breathability after heat exposure directly affects the performance of your moisture barrier, but it can also indirectly affect the performance of your thermal liner. If the moisture barrier is compromised, the thermal liner may not be as dry or it may take longer to dry out. Therefore, the moisture barrier manufacturer’s test data from before and after heat exposure can be a useful tool when selecting the best combination of components for your gear.
It is important to ensure that each component of your turnout gear maintains adequate performance (whether it is strength, insulation or breathability) throughout the life of your gear.
Kevlar® and Nomex® are registered trademarks or trademarks of E. I. du Pont de Nemours and Co. or its affiliates. PBI and design are trademarks of PBI Performance Products. CROSSTECH, GORE and design are trademarks of W. L. Gore & Associates, Inc.
PAUL DACEY is a product development engineer with W. L. Gore & Associates, Inc. For more than 19 years, Dacey has developed new technologies and products for fire, public safety and military professionals, with an emphasis on CROSSTECH® moisture barriers. Dacey holds a bachelor of science degree in mechanical engineering and a master of business administration from the University of Delaware.