Friday, 30 April 2010

Moisture Management Garments

Moisture management is one of the key performance factors in today’s garment industry, particularly in the past in the performance market; it is also becoming very important in the workwear market as well.

Moisture Management is defined as the ability of a garment to transport moisture away from the skin to the garment’s outer surface, where it can be dissipated by evaporation. This action prevents perspiration from remaining next to the skin. In hot conditions, trapped moisture may heat up and lead to fatigue or diminished performance. In cold conditions, trapped moisture will drop in temperature and cause chilling and hypothermia. Excess moisture may also cause the garment to become heavy, as well as cause damage to the skin from chafing.

In some areas of workwear, particularly where utility vests or bullet proof vests are being worn i.e. armed forces or police, the use of wicking garments under the vests reduces the fatigue and stress that operating in high temperatures or high activity can cause. This also applies to firefighters who benefit from wearing high wicking shirts under their protective equipment.

Moisture is transported in fabrics by capillary action and is commonly known as wicking. In fabrics, the spaces between the fibres effectively form tubes, which act as capillaries, and transport the liquid away from the skin. As a rule, the narrower the spaces between the fibres in a fabric, the more effectively they will draw up moisture. For this reason, fabrics with many narrow capillaries, such as microfibre, are ideal for moisture transport. Cotton has the ability to wick moisture away but also has a relatively high absorbency level that leads to the perspiration being trapped in the fabric.

Cotton can be treated with chemicals in the finishing process to reduce the level of absorbency, but this treatment may not withstand repeated laundry processes. However cotton exhibits very similar drying times as that of many of the fabrics produced from artificial fibre of which the most common in moisture management garments is polyester. The drying rate of one of the leading branded fabrics is 0.028 grams of water per minute and cotton is 0.026 grams of water per minute.

Thickness of the fabric is a key and controlling variable when it comes to moisture management; the thicker the fabric, the more moisture it holds, Most of the synthetic fabrics, like those made from microfibre polyester, were considerably thinner than cotton fabrics. However if the cotton fabrics are knitted using fine yarns then the thickness is greatly reduced.

In terms of feel a polyester fabric can in fact feel damp and clammy after drying for 90 minutes, a cotton fabric feels dry after 60 minutes, this is due to the low moisture regain of polyester of about 0.5%; cotton has a moisture regain of 8%.

Bi-component fabrics composed of a non-absorbent fibre on the inside and an absorbent fibre on the outside, have proved to be an extremely efficient construction for moisture management fabrics. This is because the absorbent material on the outside draws the moisture away from the skin while the non-absorbent material keeps the skin dry.

With this in mind Granite Workwear feature a high wicking Polo shirt and a T shirt that was developed by Texline Ltd to incorporate the best properties of microfibre and cotton.

The shirts use an inner face of Tactel that is used as a moisture transport to remove the perspiration quickly into the outer layer of cotton where it evaporates. The fabric has a very soft feel next to the skin, looks appealing on the outside as it is cotton and therefore looks natural. It also holds its shape well and has a maximum shrinkage of 2% and a 0% spirality. These garments are used as standard issue in a number of Fire Brigades and Police Forces throughout the UK. They are also extremely cost effective compared to many of the garments made using branded fabrics.

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.