Hur man skär rörisolering av fenolskum med aluminiumfolieskikt  - Sollex Blog
Johan Falk

How to Cut Foam Pipe Insulation with Aluminum Foil Layer

Kingspan Kooltherm pipe insulation Ø55mm and 100mm as an example

An important customer contacted us with the question: Do you have any knives or knife blades suitable for cutting phenolic foam pipe insulation with an aluminium foil layer? Generally about cutting insulation material The immediate response was that we should have but we were amazed at how hard the material wears on the blades. Our standard insulation knife blades 251 and 261 which are usually fantastic for rock wool insulation and foam plastic didn't really work because they are too thick and stick and crumple the foam. 

Difficulties in cutting phenolic foam insulation 

A long thin knife blade should be best. This is because the least amount of force is needed to penetrate the foam and a thinner worn knife blade retains its sharpness better compared to a worn thicker knife blade. The combination of sharpness and durability is required to penetrate the phenolic foam but also to retain the sharpness to cut the reinforced aluminium foil layer.

What is phenolic foam? 

Phenolic foam is a good insulating foam. It is a thermosetting resin or a phenolic resin equivalent to bakelite. Phenolic foam is made from phenol and formaldehyde and has a light pink-brown color. Thermosets do not melt but burn like solids. The materials are also in some cases what is known as self-extinguishing, so that the fire in the foam goes out unless energy is continuously supplied, e.g. by the continued burning of adjacent burning materials. The evolution from PUR to PIR and then phenolic foam has resulted in materials with better fire properties than ordinary foam.

Why is phenolic foam used for insulation? 

Kingspan Kooltherm rörisolering

The key issue for an insulation material is its poor thermal conductivity. Thermal conductivity is measured in W/mK (watts per metre Kelvin) and is referred to as the lambda value (λ). The lower the λ value, the poorer the thermal conductivity and the better the insulation performance.

Mineral wool in glass or stone wool has λ=0.034-0.040. Mineral wool has good sound insulation properties and is fire resistant. The disadvantages of mineral wool are that the material lacks moisture buffering capacity and can condense moisture which runs down and damages wooden structures. The fibres of mineral wool are unpleasant and the fibres can become detached and end up in the lungs through inhalation. In addition, mineral wool can smell bad and emit dangerous gases in the event of a fire. Insulation materials with phenolic foam have certain advantages. Kooltherm and SAFE-R, for example, have a lambda value of 0.020, which is almost twice as good as materials such as mineral wool and foamed plastic. This means it insulates better and you can reduce the thickness of a wall by about 30 to 50%, which is an economic advantage because living space is valuable. Insulation materials with phenolic foam also have good fire properties and can be produced in a more climate-friendly way than mineral wool. Another important factor is that phenolic foam has a low weight and high load-bearing capacity.

Different phenolic foams to cut 

Kingspan Insulation is a company that manufactures insulation materials. In Sweden they have a factory in Jönköping where they produce Kooltherm which is an insulation based on phenolic foam and Bakelite. Other insulation materials with phenolic foam are Therma, KoolDuct, Optim-R and SAFE-R. Phenolic foam insulation materials are very light due to their compact cellular structure. They are relatively easy to cut or saw but still create dust that can be harmful to breathe. To minimize dust, Sollex recommends cutting the phenolic foam with a knife blade rather than sawing with a toothed saw, which creates dust that should be avoided.

Why phenolic foam is difficult to cut 

Two things make phenolic foam insulation difficult to cut. The material wears extremely on the knife blade so when the knife blade reaches the aluminium layer it is dull and tears the reinforced foil creating dust. If the foil tears, it also means that important insulation is lost around the pipe.

Cutting pipe insulation in phenolic foam 

The most important thing is to have a really sharp knife blade. The blade should be thin so that it does not get stuck in the phenolic foam. The thickness of the blade should not be more than 0.5 mm. This means that the Sollex knife blade 251 for cutting cellular plastic is a bit too thick and unfortunately gets stuck in the phenolic foam before the reinforced aluminium foil is torn apart. A regular snap-off blade feels appealing because of the thickness and sharpness. However, there is a risk that segments of the blade will break off and injure the user. Therefore, Sollex recommends cutting blades without segments for cutting phenolic foam insulation material with reinforced aluminium foil. Sollex 180LUS (blade without segments) provides neat precise cuts with perfect surface and minimal dust.

Break blade without segment 18mm 10pcs 180LUS

Snap-off blade without segments 18mm 10pcs

Use one blade per cut and change blades when you have made a perfect cut in the pipe insulation. Probably the blade will last a few more cuts but you don't want to take a chance as a dull blade will not get through the reinforced aluminium foil, crumbling the phenolic foam and creating dust. Use good quality knife blades that are not worn out halfway into the phenolic foam.

Cutting pipe bends for phenolic foam pipe insulation with reinforced aluminium foil To cut a 90-degree angle on a pipe bend in phenolic foam pipe insulation, cut the pipe lengthwise at a 45-degree angle. Mark the angle and slowly saw the knife blade through while following the marking. This will make one cut to make the angle into a 90 degree pipe bend. Then you reverse the cut surface and you get a 90 degree angle.

Recommendation for cutting phenolic foam pipe insulation with aluminium foil 

After testing, we found that the Sollex no-break 180LUS blade worked well for cutting the phenolic foam and reinforced aluminum foil layer. Change the blade after each cut to keep it sharp for cutting the reinforced aluminium foil.

Best result: long thin razor blade without segments


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