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What is the difference between Open and Closed Cell foam?

What is the difference between Open and Closed Cell foam?     

When thinking about spray foam insulation people often don’t realise that there are two different variations of spray foam, open cell foam and closed cell foam.

At Isothane we manufacture a market leading closed cell foam insulation as it is our belief that there are many advantages to be gained from using closed cell foam however before we explain the advantages we must first understand exactly what is meant by open cell and closed cell foam.

In open cell foam the cells within the material are broken allowing air to fill the spaces within. This means the foams have a low density with the foam having a soft, sponge like appearance. As a consequence open cell foams require significantly less material per sq metre to manufacture making them cheaper.

As the name suggest the cells inside a closed cell foam remain just that closed, this means that there are no gaps for the air to fill and so air isn’t able to pass through the foam meaning closed cell foam creates an air tight barrier. Closed cell foam has a much higher density than open cell and is a more solid in structure.

Why choose Closed Cell?

  1. Better thermal characteristics. Closed cell foams offer considerably better insulation properties because of the much lower thermal conductivity. Open cell foams typically have a thermal conductivity or ‘K’ / Lambda value of about 0.039 W/mK, in comparison closed cell foams can offer a ‘K’ value as low 0.025 W/mK.

  2. Higher water vapour resistance. Because of the cell structure, closed cell foams permit only low levels of water vapour to pass through. This means that when insulating the outer skin of a building – whether that be any kind of roof or wall structure – vapour passage to the cold outer skin is restricted to a very much greater extent than it is with open cell foam, thereby significantly reducing the risk of interstitial condensation.

  3. Water resistance. Closed cell foams are water resistant.

  4. Better compressive strength. Because of the much higher core density of closed cell foams, they are practically rigid whereas open cell foams tend to have a very soft spongy feel to them. This means that closed cell foam can be used in certain situations to enhance the structural stability of a buildings framework.

open cell foamClosed cell foam 







Comparrison between open cell (left) & closed cell (right) as they are sprayed into a timber frame.

At Isothane we believe that when it comes to the thermal insulation requirements for many projects closed cell foam insulation is the best option as it reduces the risk of interstitial condensation and offers much better thermal characteristics.

More information

If you would like more information on our BBA and LABC approved closed cell foam insulation products Technitherm or Duratherm please contact our head office who will put you in touch with someone who can help.

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