Types of Insulation Explained: Which Should You Use?
There are six main types of insulation on the UK market, and each has a place. Choosing between them is mostly a matter of where the insulation will go, how much space you have, what you need it to do (heat, sound or fire) and what you want to spend. This guide explains each type in plain terms, where it fits and which products we stock, so you can narrow the choice before you check the numbers for your project.
Quick answer
- Loft floor: mineral wool rolls are the lowest-cost option.
- Floors, walls and roofs where space is tight: rigid PIR boards give a high level of insulation for their thickness.
- Floors under screed and thickness-critical jobs: phenolic boards are a premium rigid option.
- Below ground, under slabs and in wet situations: XPS and EPS are the usual rigid choices.
- Sound and partition walls: mineral wool slabs and rolls.
- Behind plasterboard on an inside wall: insulated plasterboard combines the two layers.
The main types at a glance
| Type | What it is | Common uses | Example we stock |
|---|---|---|---|
| Mineral wool (glass wool and stone wool) | Fibre insulation in rolls, batts and slabs | Lofts, stud walls, cavity walls, acoustic work | ODE loft roll, Rockwool RWA45 |
| PIR (polyisocyanurate) | Rigid foam board, foil faced | Floors, walls, pitched and flat roofs | Recticel Eurothane GP |
| Phenolic | Premium rigid foam board | Floors and walls where depth is limited | Kingspan Kooltherm K103 |
| EPS (expanded polystyrene) | Rigid bead foam board | Floors, external wall systems, general fill | EPS 70 board |
| XPS (extruded polystyrene) | Rigid closed-cell board | Inverted roofs, floors, below ground | Kingspan GreenGuard GG300 |
| Multifoil (reflective) | Layers of foil, wadding and reflective film | Add-on layer in roofs, walls and floors | SuperFOIL SF19+ |
| Insulated plasterboard | Plasterboard laminated to PIR or phenolic | Dry-lining solid walls and ceilings | Kingspan Kooltherm K118 |
Mineral wool: glass wool and stone wool
Mineral wool is made from spun glass or stone. It is light, easy to cut with a knife and is naturally good at absorbing sound, so it is used in loft floors, stud walls, cavity walls and acoustic partitions. It is the cheapest way to cover a large area but needs more thickness than a rigid board for the same performance. Browse our glass wool insulation, loft rolls and acoustic mineral wool.
PIR: the all-rounder board
PIR boards are the standard for many builders. The foil-faced boards we sell have a declared thermal conductivity of 0.022 W/mK, so they provide a given level of insulation in about half the thickness of a typical mineral wool roll. They are rigid, so can be cut to fit between joists or rafters and can take loads when laid under screed. See our PIR insulation and our PIR guide.
Phenolic: the thinnest option
Phenolic boards, like the Kingspan Kooltherm range, have a lower thermal conductivity than PIR, which means they need less thickness again. They cost more, so they are generally used where space is the issue, such as floors with limited depth. Our K103 vs PIR comparison shows how much thicker PIR has to be.
EPS and XPS: polystyrene boards
EPS is a lower-cost rigid board often used under floors and in external wall insulation systems. XPS is denser with a closed-cell structure, so it is used where moisture or loads are an issue, for example under slabs or on inverted roofs. They need more thickness than PIR to reach the same performance. See our PIR vs EPS vs XPS guide, our XPS boards and our EPS70 boards.
Multifoil: thin, but with caveats
Multifoil insulation is a thin quilt of reflective foil layers. Its performance depends on the air gaps either side being correctly formed and sealed, so it is usually used in addition to other insulation, not instead of it. Our SuperFOIL guide and wool vs PIR vs foil comparison cover the detail. See our SuperFOIL range.
Insulated plasterboard
Insulated (thermal) plasterboard bonds a layer of PIR or phenolic to a sheet of plasterboard, so you fix one board instead of two. It is the usual choice for lining an inside wall. See our insulated plasterboard and installation guide.
How to choose
- Where is it going? Loft floor, wall, floor, roof or partition.
- How much depth do you have? If you have little, move up the table towards PIR and phenolic.
- What is the target? Use our PIR U-value calculator or the insulation calculator to test it.
- Are there fire, moisture or sound requirements? See our fire safety guide and acoustic insulation guide.
- What is the budget? Compare cost per m² at the thickness you need, not just at the same thickness.
Our where to insulate guide shows which parts of a house to look at first.
Frequently asked questions
What is the best type of insulation?
There is no single best type. PIR and phenolic give the most insulation per millimetre, mineral wool is lowest in cost per m² and best for sound, and polystyrene suits floors and external systems.
What is the cheapest type of insulation?
Mineral wool rolls are usually the lowest cost per m², with EPS also low in cost. Compare at the thickness each needs for your target.
Which insulation is best for walls?
Cavity walls use PIR cavity board or mineral wool; solid walls use insulated plasterboard or PIR on battens. See our thickness guide.
Is PIR better than mineral wool?
PIR is thinner for the same performance, but mineral wool is lower in cost and better at absorbing sound. The right choice depends on the job.
Prices are shown ex VAT and vary, so check the product page before you order. Most orders over £400 + VAT are delivered free across England, with delivery to mainland Wales and Scotland too. Mainland Wales and mainland Scotland: Celotex insulation and Knauf loft roll have £40 ex VAT delivery on every order; ceilings have a £400 ex VAT minimum plus £40 ex VAT delivery; British Gypsum plaster and plasterboard have a £400 ex VAT minimum plus £40 ex VAT delivery. We do not deliver to Northern Ireland or the Scottish islands. Insulation and plasterboard orders have a £400 ex VAT minimum and free delivery (see delivery information). Outside England? Call us or contact us for a quote. Call us on 03330 908479 (Mon–Thu 8am–5pm, Fri 8am–12pm), email sales@insulationwarehousedirect.co.uk, or order online.