Make sure you know what you are looking for when buying a tent.
First, letâ€™s look at how waterproofness (or hydrostatic head) is measured. It is rated according to two tests and this is the same for all waterproof fabrics, such as those used for jackets and tents.
Test one is simulated rainfall, during which a fabric will be placed in a room where it rains. The fabric is rated according to the amount of time and pressure of the rainfall.
Test two is the Static Column Water Resistance Test. A column of water is placed on top of a fabric and the level at which the water begins to seep through is recorded. These results are measured in mm.
You will see fabrics rated, for example, 3,000mm, 5,000mm and 10,000m. The higher the figure the more waterproof it is. A very high quality waterproof fabric may score between 15,000mm and 30,000mm but itâ€™s important to take into account breathability as well.
Breathability is measured over a 24-hour period by the rate at which water vapour passes through a fabric. This result is scored in grams of water vapour per square meter (g/m2) or just “g”.
A higher level of breathability will give a higher “g” rate. Standard fabrics are around 5,000g.
Seams of jacket and tents need to be attached together. These can mean stitching or glueing. In addition, seams may have taping for extraÂ waterproofing.
Durable Water Repellent (DWR) coatings are applied to many jackets and tents to help with the dispersion of water. Youâ€™ll see water bead up and roll off the surface if it has been treated with DWR. To rewaterproof items see our previous feature,Â How to re-waterproof a jacket
A note about Gore-Tex
Gore-Tex is both waterproof and breathable but it is not measured in the standard mm. It is reckoned to be comparable to a waterproof fabric rated at 20,000mm to 60,000mm.
Modern tents are made from several different fabrics, including coated polyester, coated nylon and cuben fiber.
Nylon is stronger and more resistant to abrasion than polyester. But both fabrics require a coating to become waterproof.
A fabric’s denier â€œDâ€ is a rough indicator of its weight per square area. The lightest tent fabrics are 10D while a tent floor might be made of 70D.
Tent fabric coatings
Polyurethane (PU) is the most common coating for tents, especially budget tents. Itâ€™s the cheapest way to achieve a waterproof fabric with a fair amount of durability in wet conditions.
Unfortunately, PU coatings can be susceptible to hydrolysis (chemical breakup) due to the weather and sun. This renders them non-waterproof over time.
More expensive tents may have the addition of polyether in the PU formulations, which makes them highly resistant to hydrolysis.
Silicone elastomer coated nylons (or SilNylon) are used on many higher quality tents. SilNylon is very water repellent, elastic and stable in all UV and temperature conditions.Â SilNylon is also stronger, lighter and more robust than PU coated fabrics.Â Another benefit is that it is a slippery fabric, so snow slides off it easily in winter conditions.
The main drawback of SilNylon tents is cost. Silicone is far pricier than PU and it takes longer to coat the fabric. Another disadvantage is that because the silicone is slippery the seams canâ€™t be taped.Â The solution that some tent makers have come up with is to use nylon that’s coated with silicone on the outside and PU on the inside â€“ and then the PU is seam taped.Â Itâ€™s worth noting that double-sided silicone coated fabrics are lighter, stronger and more durable than PU/silicone combinations.
Cuben fiber, or non-woven Dyneema (NWD), is the lightest, strongest and most durable waterproof material used in the outdoor industry. In fact, it weighs less than half as much as most SilNylon-made tents.Â Apparently, Dyneema threads are â€œ50 to 70% lighter and 400%+ stronger than Kevlar and 1,500% stronger than steel per unit weightâ€. This fabric is then sandwiched between UV resistant Mylar.Â And unlike SilNylon, cuben fiber doesn’t stretch, which means that you don’t need to retighten a tent’s guylines as frequently.
Youâ€™ll either like this or hate it but Dyneema is translucent, so youâ€™ll see the night sky through it.
Although cuben fiber sounds too good to be true there are some disadvantages. It is very costly and it is less heat resistant than nylon so you need to take far more care when cooking inside a tent galley area.Â The non-stretching qualities can also leave cuben fibre tents more susceptible to tears.
Voice of the expert (or the plot thickens)
Clive Garrett, of OASE Outdoors, which is behind three major tent brands Outwell, Easy Camp and Robens, reports that 1,500mm is widely considered the minimum for UK summer camping, while 3,000mm is a good choice for most seasons and in Scotland.
Clive says: â€œWe would say that 3,000mm should handle everything that the UK could throw at it.â€
He adds: â€œMany manufacturers will use 3,000mm coatings for entry level tents, such as with Outwell.
â€œHowever, itâ€™s worth pointing out that if is often not the thickness of the coating that is important but the initial quality of the material. For instance, a 5,000mm coating may be needed to proof a loosely woven base fabric to obtain the same performance as a tighter woven fabric with a thinner coating
â€œI remember the late Bob Saunders (a leader in early lightweight tent design) telling me the reason he used silicon elastomer coating on his tents was the fact that it is applied cold whereas PU-coatings were applied hot and this immediately degrades a fabric.
â€œEvery additional PU-coating required to up the hydrostatic head damages the fabric more. The greater the hydrostatic head then the better the base fabric must be to handle the process and this ups the production costs and weight.â€
Choosing a tent
Much of the decision-making process will be dependent on your budget. It is also important to think about where you will camp (wild or campsite) and at what time of the year.
Spend as much as you can afford on a tent that is lighter or more waterproof. Ask the retailer for an expert to explain all the differences and read reviews on-line.
A tent is a big outlay and itâ€™s important to get it right.