If you're interested in using natural insulation but you're worried about the cost, this article is for you.

Like most people, we've become very familiar with the 'ethical premium': if you want the healthier, greener option you usually have to shell out more. But you might be happily surprised to find out how competitive natural insulation actually is.

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Celotex wall insulation. Photo by Bryn Pinzgauer (Creative Commons).

Natural insulation is price-competitive

While doing some research for a client, our Architectural Assistant Chrissy made an exciting discovery: natural insulation is now price-competitive with the artificial version, and in many cases is actually considerably cheaper.

Natural wall insulation costs far less than industry-standard artificial insulation per square metre.

However, natural insulation does require a greater thickness to provide the same thermal performance – about 75% more. Taking this into account, we have found that cavity wall insulation for a timber-framed brick building is significantly cheaper when using natural materials.

Based on quotes for two of the most popular and industry-standard products, the same thermal performance can be achieved with either 80mm thick Celotex FR5000 at £13.36 per square metre, or 140mm thick Thermafleece CosyWool at £10.07 per square metre.

Natural insulation is safer and healthier

Celotex FR5000 wall insulation is made from rigid polyisocyanurate (PIR) board, which is plastic-based with various chemical additives and a blowing agent to make it foam.

While not particularly hazardous, it is an irritant to skin, eyes and the upper respiratory system. Thermafleece CosyWool is a natural and safe product which is almost entirely sheep wool – you don't even need gloves to handle it.

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Natural insulation such as Thermafleece is made of sheep's wool. Photo by Andrew Patrick (Creative Commons).

Natural insulation is sustainable

Thermafleece insulation is natural, non-toxic, made in the UK, low-carbon and recyclable.

Other natural insulation types such as wood-fibre or hemp-fibre are non-toxic, low-carbon and recyclable too – although the place of manufacture will vary.

The Celotex product is free from ozone-depleting substances and is an energy-efficient insulator. However, the manufacturing process causes pollution and the product causes more pollution at the end of its life as it is difficult or impossible to recycle. Arguably, relying on plastics-based products is also inherently unsustainable as it supports the climate-disruptive oil industry.


It's not every day that the better option is the cheaper option. But with natural insulation, it's a no-brainer.

Did you know how competitive natural insulation is? Tweet us your views at @KoruArchitects!