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SUP, windsurf and wingfoil boardsThis is what causes the bubble or bulge in an inflatable board

Stephan Gölnitz

 · 25.08.2026

Often, owners only notice the small dent or scratch after a while, and this then causes them to feel uncertain.
Photo: Manuel Vogel
​In online forums, just as amongst friends, the question crops up every now and then: “There’s a small dent in my SUP – is that a problem?” In most cases, it isn’t a problem at all – it was already there when you bought it. The “dent” or “bubble” was simply only spotted afterwards – sometimes surprisingly late. The reason for this small, manufacturing-related cosmetic flaw is actually quite simple.
The small dent is located opposite the valve; it is a manufacturing defect and is completely harmless!Photo: Stephan GölnitzThe small dent is located opposite the valve; it is a manufacturing defect and is completely harmless!

​A dent in an iSUP – here’s why

If a small, outwardly bulging dent (or ‘bubble’) is visible on the board, then in the vast majority of cases it will be exactly on the opposite side to the valve: in other words, at the front or back of the underside. Or, in the case of SUP boards that have a mast foot mount for windsurfing, this is also on the underside, roughly in the middle of the board. During production, a hole has to be cut into the fabric for the valve or mast foot. In doing so, the drop stitch (thousands of vertical threads connecting the top and bottom surfaces) is also severed. As a result, the material on the opposite side may bulge slightly.

This is actually what every inflatable board looks like in cross-section. The top and bottom are connected by thousands of threads, which prevent the board from simply being a round sausage. These threads are missing at the valve or mast base. The laminate can therefore bulge slightly on the underside. This is shown here in a greatly exaggerated way for clarity.This is actually what every inflatable board looks like in cross-section. The top and bottom are connected by thousands of threads, which prevent the board from simply being a round sausage. These threads are missing at the valve or mast base. The laminate can therefore bulge slightly on the underside. This is shown here in a greatly exaggerated way for clarity.

Here’s how to ‘hide’ a bump so elegantly

Many manufacturers now resort to what is actually a simple trick. For example, the valve is fitted at the rear far enough forward that the fin box is positioned on the opposite side. JP-Australia fits the valve at the front of the bow: on the underside, the bonded towing eye cleverly conceals the small dent. Whether visible or not, these dents are merely a minor cosmetic flaw and are unavoidable due to the manufacturing process.

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Stephan Gölnitz

Stephan Gölnitz

Deputy Editor in Chief surf

Stephan Gölnitz comes from Bochum and had Holland as his home windsurfing territory for many years before moving to Munich in 1996 for the job of test editor at surf magazine. The materials engineering graduate worked as a surf instructor on the Ijsselmeer during his studies and competed for several seasons for the Essen sailing team in the Surfbundesliga and the Funboard Cup. He completed a traineeship at surf-Magazin in the test department and since then has actively accompanied almost all tests on the boom and for more than 10 years also as a photographer. Stephan has covered many thousands of test kilometers, mainly on Lake Garda and in Langebaan, but also in Egypt and Tobago. He gets his hands on over 100 new sails and boards every year as his company car. Privately, he prefers to surf with a foil on Lake Walchensee or “unfortunately far too rarely” in the waves. SUP is Stephan's second passion, which he pursued for several years at numerous SUP races. Today, he prefers to paddle on river tours with family or friends - even for several days.

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