Tuesday, 6 April 2010

Waterproof and Breathable Garments

Years ago waterproof clothes were just that. Waterproof! You put them on to keep out the rain. Unfortunately these mobile saunas soaked you in sweat as soon as you attempted any simple task. So, what is it all about? First, let us clear up the sweat bit, without sweat you're in trouble, a person performing tasks will naturally sweat to cool the body. The idea of a breathable garment is to allow the sweat to dissipate and keep the body dry while maintaining the body's "microclimate” i.e. the body's normal operating temperature and humidity.

These fabrics do not actually breathe. What they do is transfer body moisture vapour between its surfaces using the difference between the temperature and humidity next to the body and that of the cooler outdoors as a driving force. The sweat is picked up by your layering system which transports it to the surface away from your body. Here it evaporates to form a vapour. Because it is warmer and more humid inside your jacket than outside there is a difference in pressure across the fabric. In an attempt to equalise this difference vapour is driven across the fabric to the outside.

Garments which are waterproof and breathable help to provide wearers with greater comfort. This is obviously of benefit to the people wearing these whether for leisure activities or in their work. In terms of the provision of PPE by the employer it is also very important as this ensures that the safety of the wearer is not impacted by the introduction of excessive fatigue factors that have a negative impact on safety.

Waterproof garments are regulated by the safety standards of EN343. The standard is subdivided into three classes; Class 3 affords the highest level of foul weather protection, Class 2 provides intermediate foul weather protection and Class 1 provides the lowest level of foul weather protection. It is also divided into three classes of water vapour permeability (breathability) again Class 3 the highest to Class 1 the lowest.

The EN 343 Standard also has requirements for the tensile strength, tear strength, seam strength and resistance to dimensional change of the material. The mechanical strength requirements apply not only to the outer layer but also to all the layers that may be bonded to it. The dimensional stability is to ensure that the clothing does not lose its shape or fit.

The selection of the right Class of both water resistance and breathability can only be identified by a proper assessment of the conditions in which the garments will be used, the duration of the exposure and the precise activity involved.

Water resistance and water vapour permeability would appear to be mutually contradictory. It has proved to be a major challenge for manufacturers to produce a material which has both these properties. In the past, fabrics which offered protection from wind and rain did not breathe, and this made them uncomfortable to wear. Advances have been made in waterproof breathable technology over the past 30 years, there have been a number of fabrics developed using a laminate technology combined with close weaving techniques and coatings to achieve fabrics that exhibit the correct properties and also are light-weight and supple.

What is a laminate? A laminate is where a waterproof/breathable film is bonded by a special gluing process to a fabric. This could be to the outer fabric known as 2 layer and, in some cases, have a protective scrim bonded to the back of the film to create 3 layer lamination.

The introduction of these new waterproof breathable fabrics has greatly increased the range of choice for consumers. It has also led to greater market segmentation, as technologies have been developed for specific end uses and weather conditions.

In any garment there are areas that in construction can reduce the water resistance, for example the seams where the needle and thread puncture the fabric leaving small holes. In this case the seams are sealed using a special tape to eliminate this weakness. Also zips can leak water so it is important that to maintain integrity these be covered. The design of the hood and collar are also important to ensure that water cannot easily enter via the neck.

Staying dry is not just about keeping the rain out, it’s also about letting water vapour escape. The human body can expel over 4 litres of moisture a day; you just don’t notice it until you wear a significantly less breathable material over your skin. The best breathable yet waterproof barrier is perhaps human skin; it stops fluids getting in, yet opens up when fluid needs to get out. The higher the activity level and outside temperature the more the body sweats, so the more breathable your garment needs to be.

In this context, breathability is the ability of the fabric to transfer moisture vapour (not air) and is generally stated in terms of: Resistance to moisture vapour transfer (Ret) where the resistance is expressed as a number from a mathematical equation. The lower the value the less resistance there is and therefore the more breathable the garment is. Class 3 has a value of less than or equal to 20, Class 2 greater than 20 but less than or equal to 40, Class 1 greater than 40.

The standard also includes a summary table with recommended maximum wearing times, this takes account of the ambient temperature and a constant physical effort. It is required that the overview is reproduced in the manufacturers information leaflet for all garments with Class 1 protection. This is to inform the user about possible restrictions in the use of the garment; also marking in the garments must contain a restricted time warning.

For example at 10° C the time should be no longer than 4 hours, at 15°C 1.5 hours, at 20°C no longer than 1.25 hours and at 25°C no longer than 1 hour. As a comparison a Class 3 garment can be worn for 12 hours at 20°C.

Granite Workwear offer a range of garments in the Waterproof section manufactured in Flexothane ® these comply with EN 343 Class 3 waterproof and Class 2 breathable. In the Hi Viz Yellow Workwear and Orange Workwear sections garments of the Pulsar® and Pulsarail® ranges comply with EN 343 to both Class 3 waterproof and Class 3 breathability giving the maximum protection and comfort.

No comments: