Awning Materials - What's the difference?
1 CommentFriday, 16 October 2015 | Admin
Knowing your ProTec from your WeatherShield and your 75D from your 300D can make a significant impact on the type of caravan or motorhome you choose to buy. But what is the difference both technically and in the ‘real world’?
Let’s start at the beginning with the materials denier or weight. Ladies will almost certainly be familiar with the term denier, as it has been used for many years to differentiate the thickness and opacity of stockings and tights. It is commonly also used to explain the weight of awning and tent fabrics expressed as 75D or 150D for example. Denier is a unit of measure for the linear mass density of fibres. It is defined as the mass in grams per 9,000 meters of sample fibres.
Put in simple terms the higher the number given, the denser the fibres and the heavier it is. This should not be confused with the materials strength however, which is almost entirely related to the way the fibres are woven and the materials final coating. It is a common misunderstanding to conclude that a heavier material is strong and a lightweight material weaker – silk for example is very light but incredibly strong, ask any spider!
So if the materials denier doesn’t describe its strength, what impact does it have in a real world application? Well, there is no argument that a heavier material is more durable than a lighter one. But a lighter awning is easier to handle than a heavier one. That’s where the choice comes in. Is your need for a more durable awning or a lightweight awning, or maybe something in the middle?
Many awning and tent manufactures’ now use a combination of materials and techniques applied to lightweight fabrics to give them extra strength without increasing the weight significantly. A common process is often expressed within awning and tent descriptions as Ripstop fabrics. This material is interwoven with thicker nylon or polyester fibres in a crosshatch pattern which makes them more resistant to tearing and ripping. This fabric is easily identified by its three dimensional structure and distinctive crosshatch pattern typically at intervals of between 5 and 8mm – Ripstop fabrics are very durable with any damage contained within a small area which can be easily repaired.
One of the most common terms used in the awning industry explains the weave of the fabric itself – Oxford. Oxford Polyester is woven in groups of threads which are interlaced so that they form a simple criss-cross pattern. Each group of weft threads crosses an equal number of warp threads by going over one group, then under the next, and so on. The resulting fabric has a soft but durable finish which dries extremely quickly and resists small particles of dirt from entering between the weaves – making it ideal for awnings and tents alike.
Most modern awnings, both poled and inflatable types are manufactured using synthetic polyester materials which are strong and extremely resistant to water and wind penetration. Synthetic polyester, as the name suggests, is a man made material which can be woven as a 100% fibre, or with other substrates as outlined above. Because of its weather resistant properties many manufacturers’ use it extensively throughout their production process. In fact because it is so water resistant only Disperse dyes which are water insoluble, can be used to colour this material.
Of course, being a water resistant, manmade fabric, polyester does have one drawback. Without adequate ventilation, polyester fabric awnings and tents can suffer from condensation issues. Because it is not practical to make these items from breathable fabric, warm air trapped within the awning can very easily condense overnight with the living space. Ensuring good air flow throughout the awning will reduce the likelihood of morning condensation; however, because of the very nature of our British seasons it is not possible to completely eradicate it, especially during the spring and autumn mornings when the dew point is so close to the air temperature.
Internal awning and tent condensation is very often mistaken for leaking, however because of high volume, mass processing techniques used it is extremely unlikely that awning materials will allow water penetration. The only solution is ventilation and lots of it. On misty, damp mornings condensation is almost inevitable.
Polycotton fabrics are a closer representation of traditional tent and awning canvas materials. Polyester and cotton fabrics are woven together giving a stronger and heavier fabric ideal for larger family tents. The material is heavy and therefore not to everybody’s liking, but it is extremely strong and incredibly durable. Polycotton fabrics also have a better resistance to condensation due to their thickness and thermal insulation properties.
Other awning fabrics include Acrylic which is a synthetic fibre made from a polymer. Introduced by DuPont during the early 1940’s under the trademark of Orlon, mass production really took off a decade later. Acrylic materials are incredibly strong and naturally warm. The fibres can be spun and woven like wool or cashmere and when pigment dyed is resistant to oils, chemicals, and deterioration from sunlight exposure. Popular with full awning manufacturers where weight is not a primary consideration, Acrylic awnings are ideally suit for seasonal or permanent site products – with extra coatings applied to prevent UV material degradation.
Manufacturers use a number of different coatings and techniques to improve the materials weather resistance, durability, water runoff and UV stability. The combination and structure of the material used becomes a trademark for the manufacturers – Weathershield, a trademark of Kampa, Protec from Sunncamp and DormaTex a new material from Dorema are commonly seen examples. But new variants are seen almost every season.
Almost every awning and tent manufacturer will publish a known Hydrostatic Head for their given materials, but many consumers are left in the dark as to what this figure actually means. A sample of production material is sent for laboratory testing. These tests include subjecting the fabric to a waterproof test – commonly expressed as a Hydrostatic Head or HH measurement. In simple terms a piece of material is secured to the bottom of a long tube which is then filled with water. As the water fills the calibrated tube the height is measured at the point the water starts to penetrate the sample fabric. A material with a HH of 6000mm will hold a water column of 6 metres. All very impressive, but in real terms how waterproof is the product?
A European standard states that a fabric is waterproof at 1000mm and the Ministry of Defence commonly rate any material above 2000mm as waterproof. So why do manufacturers need to exceed these values. Simply put the Hydrostatic properties of a material become degraded overtime, normally due to UV exposure. Therefore a material with a higher hydrostatic head lasts longer and remains stable for longer, giving a much better real world performance. Of course knowing the HH of a material is important but the water column test doesn’t take into account wind and driving rain. Obviously under driving rain conditions the effective hydrostatic head of the material is reduced as the rain water is ‘driven’ at the material under wind pressure. Materials with a HH of 3000mm and above have long become the norm amongst awning and tent manufacturers and show exceptional performance even under the most inclement British weather conditions – this would be the minimum we would recommend for the average British camper.