Beginner’s Guide to Insulation Boards

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Heat loss is a growing concern for most UK homes and businesses, especially with average energy bills expected to rise over £1500 year-on-year. While households are waiting for the government pledge of £6.6bn in renewed insulation initiatives, improving energy efficiency and reducing carbon footprints should involve prompt action. 

Often, heating makes up well over half of the cost of energy bills. The good news is this can be reduced with simple measures. Roofs account for approximately a quarter of the heat lost, walls almost a half, and floors and windows roughly 15 percent each. 

Determining the problem areas in each home and installing some form of insulation can drastically lower costs.  

What Are Your Options?

When it comes to insulation, I’ve come to learn that the products and materials available offer a range of qualities to consider. You’ll want to think about factors like thermal efficiency, moisture resistance, fire protection, soundproofing, durability, and sustainability.

Traditional choices are fiberglass and mineral wool blankets and batts often seen in ceilings and floors, loose-fill and blown-in insulation in walls, ceilings, and lofts, and spray-foam insulation that is highly effective in walls, under flooring, and in roofs. 

insulation board

Rigid foam insulation has been extensively used since the 1970s, offering high thermal efficiency in various applications and a host of favorable properties, such as fire resistance, good structural rigidity, and being (mostly) eco-friendly. 

The compactness of the insulation boards on the market means they can be thinner than other options, so I back them as a great choice for tight spaces.

The Basics of Insulation Foam Boards

Rigid foam boards are rugged, dense panels made of closed-cell foam. The closed-cell construction makes them particularly strong, durable, and with very high thermal efficiency. The R-value of the material is what represents its thermal efficiency. 

They fare much better in this respect than the open-cell structure of other insulation materials. Homes and businesses with insulation foam panels can significantly reduce gas and electricity bills and maintain more warmth. 

They also help protect areas against excessive noise, prevent moisture and reduce the risk of fires.  

(If you want to be familiar with all woodworking terms, check this glossary with detailed definitions and images.) 


There are several types of insulation boards. Each is made of different materials in slightly different ways, lending them specific qualities. This will determine the type you choose for your insulating needs and the total cost you pay.  



Expanded polystyrene (EPS), often known as beadboard, is made by heating polystyrene foam beads. The applied heat or steam with pentane as a blowing agent causes the beads to fuse, creating an efficient closed-cell structure. 

Now, here’s where it gets interesting – EPS is essentially 98% air and only 2% polystyrene. The trapped air is a poor heat conductor and gives the foam excellent thermal insulation properties. 

In terms of thermal efficiency, it holds its own with an R-value of 4 per 25mm thickness, right up there with rigid fiberglass and far superior to mineral wool or fiberglass batts. Boards can come in higher density and facer/backer material, increasing thermal resistance.  

The foam also exhibits good mechanical strength (impact resistant), doesn’t deform over time, has extremely-low levels of water absorption, isn’t affected by chemicals, and is generally weather resistant. With added fire retardants, EPS also meets fire standards as it has very low ignitability and doesn’t spread flames. 


The low cost makes EPS a popular choice when insulating virtually any area in homes and buildings. EPS insulation boards are not only cost-effective but also easy to install, providing a durable and long-lasting solution for thermal insulation needs. But if you’re after the best possible performance, other options are available.  


XPS, or extruded polystyrene (aka Styrofoam), is a similar product but differs in the way it’s made. It is manufactured by liquifying polystyrene pellets, injecting a blowing agent, usually Freon, and mixing with additives under pressure. When the product cools, it creates a closed rigid cell foam.  

The production process lends XPS more compressive strength and higher density than EPS, which is preferable in flooring applications. It also has better water resistance making it ideal for roof and external wall insulation. 

When it comes to thermal efficiency, XPS doesn’t disappoint either. It boasts an R-value of 5 for the same 25mm thickness, which means you can get away with a thinner construction while still enjoying top-notch insulation. Now, the trade-off here is that these superior qualities often come with a slightly higher price tag, but in my experience, it’s usually worth the investment, especially when you’re looking for top-notch performance in specific applications.


PUR or rigid polyurethane insulation panels are made using crude oil derivatives, polyols, and isocyanates with blowing agents and other additives. When mixed, the ingredients react and foam. PUR panels have high insulation performance due to the rigid, closed cell structure, comprising 97% trapped gas and 3% polymers. 


The production of PIR or polyisocyanurate is similar but uses different blowing agents at higher temperatures. Both are thermoset plastic panels with very high R-values (6 for PUR and 7 for foil-faced PIR boards). 

Now, here’s the deal – PIR seems like a real upgrade from its PUR cousin, faring better in almost every aspect. In addition, no ozone-depleting CFCs are found in PIR panels, making this an eco-friendly alternative.  

PIR panels have very high compressive strength and impact resistance, comparable to high-density XPS, excellent fire resistance (one of the highest among all insulative materials), and don’t spread flames or smoke. They are also used with facer and backer foils as a water or moisture barrier.  

basement with hardwood flooring

The boards are ideal for insulating wall cavities, slanted and flat roofs, basements, and in different types of floors. The high thermal efficiency allows for thinner boards where space is limited (solid concrete floors). 

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Buyers will also find insulated plasterboard with a PIR core bonded to gypsum plasterboard. This can be used in insulating internal walls, pitched roofs, and lofts. All in all, PIR panels check off a lot of boxes when it comes to insulation.  

What to Look For?

When it comes to insulation rigid foam panels, I’ve got hands-on experience that can shed some light. These panels are all about their thermal resistance and high R-values, and they do come with some other perks that make them a versatile choice. In terms of thermal efficiency, they need to have the right thickness. And this affects the price. 

Similar thermal efficiency and R-values, for instance, can be achieved with a 50mm PIR and a 100mm EPS. And both will have a similar price. The limiting factor here is how much space is available. 

A savvy move, if you have the room for it, is to go for the thickest panels possible. This not only supercharges your insulation performance but also chips away at those energy bills.

sawing PIR boards

Speaking of costs, EPS panels usually win the affordability game, followed by XPS, with PUR and PIR panels often coming in at a higher price point. While price differences may be smaller for the same thickness, this adds up when insulating larger areas. 

A side benefit is that all panels come in the standard building sizes (1200mm by 2400mm), are lightweight (considering they’re mostly air), are easily manageable, and installation can be a DIY project using minimal tools or safety gear, considering woodworking safety rules. Additional gear like foils and adhesives are also cheap. 

One area where the different panels perform quite distinctly is fire resistance and flame propagation. Homes and commercial properties that need to meet strict fire standards are advised to use PIR insulation with appropriate foils.  

Lastly, make sure to source insulation boards from respected and established brands. Some popular insulation names in the UK include Kingspan, Ecotherm, Quinn, Mannok, and others. All have extensive lineups to insulate floors, roofs, ceilings, lofts, walls, and flooring.  

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Robert Johnson is a passionate furniture maker & carpenter, sought after for his knowledge on the craft.
You’ve probably seen his down-to-earth wisdom in USA Today, Bobvila, Family Handyman, and The Spruce, where he has shared commentary and guidance on various woodworking topics.

Robert is the brain behind Sawinery, where he aims to share tips, tricks, and a passion for all things carpentry.

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