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One thing we are often asked about is what the sizes quoted for pipe insulation actually mean. You will always see three measurements quoted when describing pipe insulation; wall thickness, bore diameter and length. Wall thickness is simply how much thickness of insulation you have, so for example if you have 13mm wall pipe insulation then that means you have 13mm of insulation on both sides of your pipe. This thickness is often one of the most important parts of your decision. Too thin and you may not get the results you want, but too thick and it may not fit your pipes and walls.
If you don’t have a lot of space but want to prevent your pipes from losing too much heat then you may want to go with a 13mm wall thickness of 9mm which will provide cheap and effective energy savings (but remember you have to seal the insulation properly to prevent gaps where heat can escape). If you have more space and are looking for maximum efficiency then you may want to go with a 25mm wall to get the best results.
A fairly simple rule of thumb (use it only as a rough guide) is that for energy loss the larger the pipe the thicker the insulation as it has more surface area so it will dissipate heat faster, but for freeze protection the smaller the pipe the thicker the insulation you need as a small amount of water will freeze faster. The bore is essentially the hole that the insulation pipe goes through. This is the measurement of the pipe from one side to the other and is called the diameter of the pipe. Most bores are designed to fit copper or iron pipe sizes as these are common in the UK, but if your pipe is plastic then you would generally use a size close to that. For example if you have 25mm plastic pipe then you would use 28mm bore pipe insulation; always go up a size rather than down. A little more space isn't a problem but if it's too tight it might open up even if you seal it with adhesive. If you want to double check the diameter of the pipe (measuring in tight spaces can sometimes be tricky) then you can measure the circumference of the pipe (the measurement around it) and divide this number by π, which is approximately 3.14159 if you don't have that button on your calculator.
