Seams, tear strength and water column
Creating good tent fabrics is a challenging task as there are so many different factors that need to work optimally together. Many believe that so long as a fabric has a high water column, it’s of a good quality. We believe that a combination of a high water column, high tear-strength and selecting the right seams and threads is the secret behind the best tent fabrics.
Seams are very important to the quality of a tent, and it’s essential to have the right seams in the right place. On our tents, the seams that bear the greatest strain are sewn using a felled seam or using the shuttle stitch method. Shuttle stitch is the only type of seam that doesn’t unravel if the thread breaks. Particularly load-bearing areas are reinforced using a special bartack seam. Peg loops, for example, use bartack seam and inlaid reinforcement.
The seams are positioned on the tent in such a way that water can run off easily, rather than collecting at the seam edge.
In addition to careful seam positioning, we use a continuous filament polyester thread with a water-resistant coating. This allows us to use a very thin needle which creates a very small hole in the fabric. Small holes and water-repellent thread ensure that water does not penetrate the external material.
The combination of felled seams and their positioning in relation to the poles creates a waterproof construction.
Ground sheet seams
Some tent manufacturers weld the ground sheet seams, however most of our tents are made using a silicone-treated floor sheet with no welded seams. This is possible thanks to our sewing methods and choice of thread. However, some teepees and tents require a flame-retardant ground sheet. In these cases, the seams are welded as the flame-retarding treatment becomes ineffective in when combined with silicon-treatment.
It’s important to note that tear strength is only a measure of a fabric’s ability to resist further tearing after an initial tear has occurred. A high tear thus strength increases resistance to further tearing. For tents, it also indicates how the fabric behaves along seams and around guy points, etc.
Tear strength is affected by four factors: material, thread thickness and construction and coating. The first three factors are directly linked to the fabric itself. A strong material, with thick threads and reinforcement threads in several places, has a proportionally higher tear strength. However, the type of coating used also affects tear strength even if it may be difficult to see with the naked eye.
Imagine a fabric where a tear is developing. A stiff coating, such as PU, will create uneven tension in the fabric and the threads will tear one by one. If, on the other hand, the coating used is more flexible — like silicone — the tension will be spread across more threads, dramatically increasing tear strength.
We test our materials based on the international standard ISO 139374. In our Pro and X-Trem tents we use Helsport Superlight® 1000 which, with a tear strength of more than 18 kg, is among the strongest on the market.
According to the international standard EN 343, a fabric is considered waterproof if it has a water column rating of 800 mm. However, in a new fabric, the fabric’s ability to retain a high water column rating over time is more important than the initial water column. The water column is measured by exposing a fabric sample to increasing water pressure. The test is stopped once three droplets of water have passed through the fabric.
Essentially, a water column of 800 signifies that a material is waterproof. However, the water column rating required will differ based on the fabric’s use. For outer tents, a water column of 800 will make the fabric resistant to rain in very windy conditions, but you’d need a higher water column if you were to sit on the ground sheet of a tent that was placed on wet ground. Helsport has therefore chosen a fabric with a higher water column rating for the ground sheet material than for the outer tent.
Silicone and PU coatings degrade over time and sunlight, folding and bending will lead to a reduced water column rating. It’s therefore a good idea to start with a water column higher than 800 mm, to ensure the product a long lifespan.