Seams, tear strength and water column
Producing high quality tent fabrics is challenging, as there are many different factors that need to work together optimally. For example, many customers judge a fabric’s quality based simply on its water resistance. We think the best fabrics have a combination of three key factors: a sufficiently high water column; a high tear strength; and correct choice of seam and thread.
Seams are crucial for a tent’s quality, and seam placement is important. Seams with the greatest strain are sewn with double-needle stitching, creating the only kind of seam that stays connected even if a thread is broken. Other load-bearing points, for example the peg points, are reinforced with a special bartack seam. The seams on the tent are placed and oriented so water can run off easily, rather than collecting at the seam edge.
The type and placement of the seam, relative to the poles, results in a waterproof construction.
In addition to a well-considered seam placement, we use a continuous filament polyester thread with WR coating. This allows us to use a thinner needle, resulting in smaller stitching holes. This combination of water repellent thread and smaller holes prevents water moving through the fabric.
Seams in the floor
Our tents are made using a silicone-treated floor sheet with no welds, a point of difference to other producers. Using our waterproof threads and sewing techniques, our seams remain waterproof even without welding. However our lavvus and TREK tents, with their flame-retardant treatment, cannot be treated with silicone and hence have welded seams.
It’s important to note that tear strength describes a fabric’s ability to resist further tearing after an initial cut. A high tear strength increases resistance to further tearing. For tents, this also affects how the fabric behaves along seams and around guy points etc.
Tear strength is affected by four factors: material, thread thickness, construction, and coating. The first three factors are directly linked to the fabric itself, in which a strong material, with thick threads and reinforced construction, gives a proportionally higher tear strength. But how does the coating affect tear strength?
Picture an area of a fabric where a tear is developing. A less flexible coating, like PU, will lead to an uneven tension in the fabric and the threads can tear one by one. If, on the other hand, the coating is more flexible, like silicone, the tension will spread more evenly across more threads dramatically increasing tear strength.
We test our materials using the international standard ISO 139734. In our PRO and X-TREM tents we use Helsport Superlight® 1000, which, with a tear strength of over 18 kg, is among the strongest on the market.
According to the international standard EN 343, a fabric is considered waterproof with a water column rating of 800 mm. However, more important than the water column for a new fabric is the fabric’s ability to retain a high rating over time.
The water column is measured by exposing a fabric sample to an increasing water pressure. The test is halted when 3 droplets of water have passed through the fabric sample.
Different areas of use require different water column ratings. The outer tent needs resistance against rain, wind and snow, but is exposed to a totally different water pressure than the floor, which might be pressed down against wet ground. Helsport has therefore chosen a fabric with a higher water column rating for the floor than for the outer tent.
It’s important to also note that silicone and PU coatings degrade over time. Bending and creasing of the material and exposure to UV rays from the sun will lead to a reduced water column rating. By starting with a higher rating than 800mm, the total lifetime of a tent is increased.