Insulation types

Materials and comparison

If you are considering installing modern energy and heat generation in your property, e.g. solar panels, heat pumps etc. then you could be wasting a lot of money unless you also increase the efficiency of your property via insulation, double glazing, draft exclusion etc.

Types of insulation:

Rigid insulation (boards)

• PIR – Polyisocyanurate  – (Celotex, Kingspan). This is a lightweight firm insulating board made of two aluminium facings with PIR insulation between. Various thickness are available.
• PUR – Polyurethane. Similar type of board but less efficient. (Also available as spray on foam  – see below).
• Expanded Polystyrene board.
• Woodfibre. One of the oldest forms of manufactured insulation. This is coming back into fashion as an environmentally friendly and breathable material.

Batting/blanket

• Fibreglass or mineral fibre insulation blanket. Readily available in rolls. Typically sold for topping up loft insulation
• Recycled polyester blanket e.g. from plastic bottles. (Non-itch and Supasoft) more environmentally friendly and less itchy alternative to the above
• Sheepswool. Usually a combination of actual sheeps wool and other materials such as recycled polyester.
• Hemp wool. This is becoming more popular as it is made from natural materials.

Other

• Polystyrene beads used for blowing into wall cavities as a retrofit.
• Multifoil (e.g. Superquilt). A very thin blanket made of foil layers which work only in combination with a sealed air gap on one or either side.
• Aerogel (sold under the brand name Spacetherm). A highly efficient insulator developed by NASA. It is useful in very thin layers which can provide more insulation to other types of insulation. Available in blankets, or with a boarded backing.
• Insulating plaster. Plaster mixed with polystyrene or cork. Better thermal resistance than normal (gypsum or lime) plaster but not hugely effective. (R-value .22 per 10mm)
• Spray on foam (polyurethane). Now widely discouraged as it can seal in damp and mouldy timber work. Mortgage companies now sometimes refuse loans when this is used on a property.
• Thermal wallpaper Available in various materials (e.g. expanded polystyrene, rubber) and thicknesses from 2mm – 10mm. This is an easy DIY retrofit for internal wall insulation however the actual benefits are small compared with the cost.

As you can see there is a lot of choice, and there are still, products we haven’t mentioned.

Comparing types of insulation

Understanding how insulation is measured can be a bit confusing as there are different types of measurements, all of which seem a bit baffling to non-scientists. Although you may often hear about U-value it is less useful when comparing products because it is mostly used when considering a whole structure, e.g. a wall, and is calculated from all the elements involved including masonry, cladding, stud work, render and insulation.

The typical values you will see on product specifications are Thermal Resistance (R-Value) and Thermal Conductivity (K-value or λ-value). The symbol λ is pronounced “lamb-da.”

If you are interested how these values relate to each other read on. Otherwise you can skip this bit go straight to the Comparison chart. The important thing to know is that for good insulation high R-values are best and low K-values and U-values are best.

• R-value = thermal resistance (m²K/W) This means how good the material is at stopping the heat leaving your house, so higher numbers are good. The R-value depends on the thermal efficiency as well thickness of the material. For example 100mm insulation that has an R-value of 2.5 will have an R-value of 5 if it is doubled up to be 200mm. This is the main measurement we will be using to compare different materials as it is readily available from manufacturers and retailers.
• K-value (or λ-value) = thermal conductivity (W/mK) The rate at which heat flows through something so low values are better. As this is a rate of flow it is not dependant on thickness of but is a good indicator of the overall thermal efficiency of a material.

If you know the thermal conductivity and thickness you can calculate the thermal resistance, and vice versa

• R = metre thickness ÷ K
• K = meter thickness ÷ R
• U = 1 ÷ R . However, as mentioned, U-value is rarely used for single materials but relate to a whole structure, roof or floor so the R-value used is the sum of the different materials’ R-value

For a much more in-depth scientific explanation see Insulation Outlook

Convert Thermal resistance to thermal conductivity and vice versa Online calculator

Comparison chart

The tables below should be taken only as a rough guide. Materials can perform better or worse depending on the application and appropriateness of the installation. The prices quoted may be very approximate depending on the supplier, quantities ordered and  delivery. We have not included installation costs. Some products need extra materials and fixings. However as a very rough guide this can give you an idea of your options when considering a basic DIY retrofit insulation project such as insulating a loft floor.

One of the main things we can take from this is that PIR is approximately twice as efficient as most of the soft “batting” or blanket type insulation. The R-value of 4.5 for 100mm is about twice the thermal resistance for the same thickness of fibreglass roll. The  λ-value (=thermal conductivity: not related to thickness) is about half.

*Airtec and superquilt are designed to be used in a system with sealed air cavities either side. The R-value given here assumes 25mm cavity either side. It makes little sense to provide a λ-value.

How much insulation to do a loft to building regulation standards?

The current building regulations for roofs require a minimum U-value of >0.11. In order to achieve this comfortably a realistic R value for the insulation alone is about 7. In real life it may be necessary to fit more than the required thickness depending on the availability of different thicknesses of the material itself. The last column shows the cost per metre required to achieve an R-value of 7.

*Note that these equations do not work in regard to Superquilt or Airtec as it is a system that relies on different materials and air gap, so in order to achieve building regs there is a special triple layer system.

Some conclusions to achieve roof building regulations of U-value 0.18

• Most types of batting = approx 270mm – these are usually available in thickness of 100mm, 170mm or 200mm.
• PIR =approx 150mm
• Aerogel = approx 97mm. This is extremely expensive and so not very practical.
• Sempatap = approx 335mm. This is 33.5 layers at 10mm so is neither practical nor economical at £729 m^2..

Aerogel and Sempatap are not practical, we have only included them to demonstrate this.