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One thing we are often asked is what the dimensions referenced in pipe insulation actually mean. When describing pipe insulation, you will always see three measurements referenced; wall thickness, bore diameter and length. Wall thickness is simple, it is how much thickness of insulation you have. Therefore, for example, if you have 13mm wall pipe insulation, then this means you have 13mm of insulation on both sides of your pipe. This thickness is usually one of the 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 much space but want to prevent the pipe from losing too much heat, then you may need to use 9mm or 13mm wall thickness, which will provide cheap and effective energy savings (but remember, you must properly seal the insulation to prevent gaps where heat escapes). If you have more space and are looking for maximum efficiency, then you may need to use 25mm wall for optimal results.
A fairly simple rule of thumb (used only as a rough guide) is that to prevent energy loss, the larger the pipe, the thicker the insulation, because it has a larger surface area and therefore dissipates heat faster, but for freeze protection, the smaller the pipe the thicker insulation you need, because a small amount of water will freeze faster. The bore diameter is essentially the hole through which the insulation pipe passes. This is the measurement of the pipe from one side to the other, called the pipe diameter. Most bore diameters are designed to fit copper or iron pipe sizes because these sizes are common in the UK, but if your pipes are plastic, then you will usually use a close size. For example, if you have 25mm plastic pipe, then you will use 28mm bore pipe insulation; always go up a size rather than down. A little more space is not a problem, but if it is too tight, it may open even if you seal it with adhesive. If you want to carefully 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.
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