How flat-sided oval profile steel tube delivers strength where your polytunnel needs it most
At first glance, many polytunnels appear similar. Frames often look alike, covers look alike, and specifications can seem comparable. However, one of the biggest structural differences, and one that’s rarely discussed, is the shape of the steel tubing used to form the frame.
Round Tubes vs Flat-Sided Oval Tubes
Many standard polytunnels use round steel tubes, typically around 50 mm or 60 mm in diameter for commercial polytunnels or 25mm to 35mm for domestic polytunnels.
Northern Polytunnels uses flat-sided oval (FSO) tubes in the hoops of EasyBuild domestic polytunnels and EnviroPro commercial polytunnels. The oval profile delivers increased strength where it matters most, on the sides of the tunnel where wind loading is greatest, helping the frame resist bending, flexing, and deformation during strong winds or heavy weather.
Testing shows that flat-sided oval profiles can provide up to 150% greater strength compared with equivalent round tubing, which is why they form a core part of our structural design.
Watch the video below to see a demonstration of the increased strength that Flat Sided Oval tubes provide.
Frequently Asked Questions
What does FSO mean in polytunnel construction?
FSO stands for Flat-Sided Oval. It refers to the shape of the steel tube used in the polytunnel frame. Unlike standard round tubing, the flat-sided oval profile is engineered to increase structural rigidity and reduce flex under load.
Why are flat-sided oval tubes stronger than round tubes?
Flat-sided oval tubes place more steel where the loads are greatest – from wind on the sides of the tunnel – so they bend and flex far less than traditional round tubes, creating a stronger, more stable polytunnel frame.
Why are flat-sided oval tubes stronger than round tubes?
Flat-sided oval tubes are used for the hoops of the polytunnel where strength and rigidity are most important for overall stability.
Does tube shape really make a noticeable difference?
Yes. Even when two frames use similar steel thicknesses, the shape of the tube can significantly affect how much the structure flexes under wind or load. Reduced movement helps improve long-term durability and growing stability inside the tunnel. Our tests revealed that FSO can provide a 150% strength improvement compared to round tube.
Are FSO tubes used in both domestic and commercial polytunnels?
Yes. Flat-sided oval tubing is used across both domestic EasyBuild polytunnels and commercial EnviroPro structures, ensuring consistent structural performance across the ranges.
Will stronger tubing increase the lifespan of a polytunnel?
A more rigid frame experiences less movement over time, which reduces wear on the structure and the cover, helping contribute to a longer overall service life.
