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Which Is The Best Type Of External Wall Insulation?

There is no definitive answer to this question. All four of our EWI external wall insulation systems provide benefits to their customers, some more suited to the needs and requirements of the project than others. Our technical team is always on hand with expert advice to suggest the best solution. So which will they suggest to you?


The premier solution is Rockwool, a mineral wool composed of volcanic rock and compiled to form slabs in a similar way to that of candy floss. The standout feature of this product is its complete non-combustibility, having achieved a Euroclass rating of A1. Rockwool can withstand temperatures of up to 1,000ºC, prevent the spread of fires, and not emit any toxic emissions. The acoustic insulation and dual density composition are further benefits to an already high performance system. Rockwool is also breathable! In turn, this allows trapped moisture in the existing wall to pass through the insulation and dissipate into the atmosphere, assuming a breathable Silicone render is used.


Kingspan Kooltherm K5 offers a highly effective and space-saving solution. The rigid phenolic core of the K5, bracketed by a glass tissue board, offers excellent thermal capabilities. Space saving features of the K5 make it the ideal choice for narrow passageways and alleys. The high compressive strength also ensures that any risk of mechanical compression and impact is minimised. External wall insulation as a rule reduces the households carbon footprint, with K5 boards also having an ozone depletion potential of zero.


EPS is the most popular external wall insulation, offering great value for money and still providing excellent thermal performance. The whole system is extremely lightweight, meaning that the cost for installation materials is far lower than Rockwool or K5. EPS has been designed specifically to be applied onto masonry or timber-backed walls using adhesive and mechanical fixings. They can also be installed in the cavity void if the property is being insulated using cavity wall insulation.


XPS or extruded polystyrene board is a high-density board that can be used for various applications on buildings, including DPC insulation, extending concrete window sills or providing insulation backing where EPS is not suitable to use. Being compact and robust means that XPS is easy to store and reduces the risk of water penetration.

You can review the product’s properties in our handy comparison table!

Euroclass ratingA10BEE
CompositionDual density mineral woolPhenolicexpanded polystyrene, graphiteextruded polystyrene, silver boards
Acoustic insulation
Thermal conductivity0.036W/(m2K)0.020W/(m2K)0.032W/(m2K)0.034W/(m2K)
R-value1.39W/(m2K)2.5W/(m2K)1.97W/(m2K)3.33W/(m2K) (100mm)
Water vapour resistivity1.2% water absorption300MN.s/g.m145-238MN.s/g.m
Compressive strength10 kPa120kPa70kPa130kPa

Contact our technical team on 0204 5719697 today for the best EWI solution! They will happily advise on how to lower your energy bills.


6 thoughts on “Which Is The Best Type Of External Wall Insulation?

  1. I would like to know the difference in price or even which is the overall best quality , cost effective type of external insulation to use?

    1. Hi Kate, EPS is often thought of as the most cost effective because of the great thermal performance at a lower cost. You need to achieve a benchmark of 0.3W/m2K so you need a different thickness for each insulation board.

      We’ve discussed the price of our different boards here: Comparing EWI & Price Impact

      As a rough per board guide:
      EPS – 90mm required = £8.25 ex VAT per board
      K5 – 60mm required = £15.80 ex VAT per board
      Rockwool – 110mm required = £21.50 ex VAT per board

      Are you looking to insulate your property?

  2. Which is the best value product to use when undulating from inside the house on an external wall without compromising on efficacy? I need to do two bedrooms and a bathroom.

    1. Hi Shazzy, with internal wall insulation, saving space is usually the main concern because you want to impact as little of the internal floor area as possible. Kingspan K5 is a great space saving system but it can be a little expensive. EPS is the best value but you’ll need around 90-100mm to bring your walls up to regulations. Is there an option for the walls to be insulated externally?

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