In the run up to some particularly warm weather, I became concerned at how hot the framework became on my polytunnel. I was a little worried about the potential of burning my skin or, worse, my young daughter's against the extremely hot metal. I also realized that having a hot frame next to the polyethylene cover was not likely to do it any good.
I did lots of reading about how to remedy this issue. You can extend the life of the cover or the polyethylene over the top of the framework by creating a barrier between the two. The usual fix is to use something that is known as anti hotspot tape. I found a solution which works better for our needs.
About Anti Hotspot Tape
You can buy a product commonly known as anti hotspot tape. This creates a bit of a barrier between the metal bars of your polytunnel frame and its polyethylene covering. The tape comes on a roll with an adhesive on one side and a foam backing on the other. You cut off strips and place them where you want on the bars of the polytunnel. To do a really good job of creating a barrier, you need a lot of tape. It can also degrade and lose the adhesive backing over time which renders it useless as a permanent solution.
I believe that anti hotspot tape can help to extend the wear and tear on your cover. It can prevent the covering from chaffing up and rubbing against the metal bars in the wind. The friction caused by this will eventually result in holes and weak spots forming. It can also help to prevent heat degradation which occurs when the frame gets extremely hot from the summer sun shining on it for extended periods of time. The idea of it is sound and using the tape should help your cover to last longer and increase its limited shelf life.
I wasn't keen on using the tape for a few reasons. Firstly, it is pretty expensive if you want to use it all over your polytunnel frame. Secondly, I wasn't convinced at how long the sticky adhesive would last before starting to peel off. It seemed to me like this tape would be a shorter term solution and something that we'd need to buy again in maybe a year or two.
Using Pipe Insulation as an Alternative
Cautionary note: Adding pipe lagging or insulation to your frame may cause the polyethylene of your polytunnel to become very tight if you have a fitted cover. This could then cause the cover to weaken around the seams. You can use the idea with caution and some common sense for what works in your particular situation.
I used this pipe lagging in the hottest part of the summer while the doors on the cover were permanently rolled up. Having the doors open makes the cover a looser fit. I was then able to remove the insulation very easily once the weather cooled down.
We bought 25 meters of pipe insulation which was enough to cover all the frame of our particular Gardman Polytunnel except for the bars at the very base. The framework at the base does not tend to get as hot as the bars nearer the top so plan to cover the top bars first and those exposed most to the sun. The lagging is nice and thick and merely slips over the piping on the frame. It does not rely on any adhesive as with the tape which means that you can easily take it on and off as needed. Lagging is also durable and should last for many years.
We bought our pipe insulation from Wickes which is a trade DIY store here in the UK. It is 22 mm in diameter with a 13 mm thickness of foam. This was the right size to fit the framework on our polytunnel. We also tested a piece out on the frame before we committed to buying 25 meters of it. Depending on your own polytunnel, you may need a different sizing to fit around the frame.
Fitting the Pipe Insulation
This pipe insulation we used comes in 1 meter lengths. It's like a foam tubing which has a slit down one side of the length. You need to carefully pull apart the cut section with your fingers. My husband is demonstrating opening up the lagging in the photo above.
You slot the open side of the pipe insulation over your polytunnel bars and hoops as needed. To do this job, it is best if you completely remove the cover first. You can also fit the insulation on before fitting a cover with a new polytunnel. The cover on ours was loose enough to put on the pipe insulation while it was still in place.
The lagging is very easy to slot on. I recommend leaving the lengths uncut to start with. Work from the top of the frame which seems to attract the most heat from the sun. Alternatively start with the areas that are most affected by the sun's heat. I added whole lengths everywhere except for the very base of the framework and then started cutting pieces to size as needed.
This Solution is Easy to Install and Use
You can see the insulation on the framework in this photo of my polytunnel. I love that it is a perfect size and it fits well. There is no adhesive which might disintegrate at some point and the lagging is easy to slip on and off the bars as needed.
It was a bit of a squeeze to get the cover back in place. If you have openings like doors with zips, you need them fully open while putting the cover back on to prevent damage to seams. I'm very happy with this as an alternative to anti hotspot tape and the burning hot metal is now carefully kept away from the vulnerable polyethylene covering. Hopefully this will help to keep the cover going for a bit longer before we need to replace it.
Image Credit: all images on this page belong to the author of this article, Marie Williams Johnstone