Insulation types explained

Learn the main types of insulation, what they're for, and how to avoid the mistakes beginners make when choosing or handling them.

IN-01Understand what insulation actually doesInsulation doesn't make heat, it slows heat moving from warm to cold. In winter that means less heat escaping your home; in summer it means less heat getting in. The main number to look for is the R-value: the higher the R-value, the better it resists heat flow for a given thickness.

IN-02Know the three main insulation familiesMineral wool (glass wool or rock wool) is the yellow or grey fluffy roll or batt, cheap, fire-resistant, but itchy to handle. Rigid foam board (PIR or EPS, often shiny-faced) gives better insulation for a thinner layer, so it suits tight spaces, but it costs more. Natural fibre (sheep's wool, wood fibre) breathes well and is pleasant to handle, but is usually the most expensive option.

IN-03Learn why the shiny or foil side mattersSome insulation has a foil or plastic facing on one side, called a vapour barrier. This stops warm, moist air passing through and turning to condensation inside the insulation, which can cause damp and rot. The beginner mistake is fitting it the wrong way round, so always check the packaging for which side should face the warm room.

IN-04Read the packaging before you buyThe pack tells you the R-value, the thickness, and what it's designed for, such as loft floor, wall cavity, or pipe lagging. Using the wrong type in the wrong place is a common mistake, for example loft roll used to wrap a pipe won't perform the same way. Match the product to the job, not just the price.

IN-05Handle mineral wool safelyMineral wool sheds tiny fibres that irritate skin, eyes, and lungs. Wear gloves, safety glasses, a dust mask, and long sleeves before you touch it, and work in a ventilated space. Wash exposed skin afterwards rather than rubbing it, which pushes fibres in further.

IN-06Avoid the squashing mistakeInsulation works by trapping air, so squashing it into a gap that's too small ruins its performance, sometimes by half or more. It's better to trim material to fit loosely than to force too much into a tight space. Gaps around the edges are just as bad, since heat escapes easily through any unfilled space.

IN-07Check you've got it rightGood insulation looks even, sits at full thickness with no squashed patches, and has no gaps at joints or edges. Any vapour barrier faces the correct way as stated on the pack. If you can see daylight through a join, or the material springs back thinner than the stated depth, it needs adjusting.

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