Kingspan K118 vs Celotex PL4000 Insulated Plasterboard Compared
Insulated plasterboard lets you insulate and dry-line a wall in one step: insulation bonded to plasterboard, fixed to battens, studs or with adhesive, then taped and jointed or skimmed. Kingspan Kooltherm K118 and Celotex PL4000 (now sold as Sopratherm PL4000) are two boards we stock. K118 uses phenolic insulation and PL4000 uses PIR, which changes how thick the finished wall is and how you buy it. This guide compares them using the manufacturers' data shown on our product pages.
The two boards in brief
- Kingspan Kooltherm K118: phenolic insulation bonded to 12.5mm tapered-edge plasterboard, for internal dry-lining of walls and ceilings. Declared thermal conductivity 0.019 W/mK. Sold in full manufacturer packs only.
- Celotex PL4000: PIR insulation bonded to 12.5mm tapered-edge plasterboard, for dry-lining walls with dabs and mechanical fixings or on timber or metal studs. Declared thermal conductivity of the PIR core 0.022 W/mK. Sold per sheet.
Both are 2400 × 1200mm sheets (2.88m²). The insulant thickness is the number before “+ 12.5”. Browse all insulated plasterboard.
Side-by-side comparison
| Kingspan Kooltherm K118 | Celotex PL4000 | |
|---|---|---|
| Insulation core | Phenolic | PIR |
| Thermal conductivity (λ) | 0.019 W/mK | 0.022 W/mK |
| Plasterboard | 12.5mm tapered edge | 12.5mm tapered edge |
| Reaction to fire | Insulation B-s1,d0; plasterboard A2-s1,d0 | B-s1,d0 (62.5mm board, per Soprema; check the datasheet for other thicknesses) |
| Overall thicknesses we stock | 37.5, 42.5, 52.5, 57.5, 62.5, 72.5, 82.5mm | 37.5, 52.5, 62.5, 77.5mm |
| How we sell it | Full packs only (9–21 boards) | Single sheets |
Thermal resistance by thickness
R-values from the manufacturers' datasheets as shown on our product pages (Kingspan quotes K118 for the insulant only).
Kingspan Kooltherm K118
| Board (overall, insulant + board) | R-value (m²K/W) | Sold as |
|---|---|---|
| 37.5mm (25 + 12.5) | 1.30 | Pack of 21 |
| 42.5mm (30 + 12.5) | 1.55 | Pack of 18 |
| 52.5mm (40 + 12.5) | 2.10 | Pack of 15 |
| 57.5mm (45 + 12.5) | 2.35 | Pack of 14 |
| 62.5mm (50 + 12.5) | 2.60 | Pack of 12 |
| 72.5mm (60 + 12.5) | 3.15 | Pack of 11 |
| 82.5mm (70 + 12.5) | 3.65 | Pack of 9 |
Celotex PL4000
| Board (overall, insulant + board) | R-value (m²K/W) | Sold as |
|---|---|---|
| 37.5mm (25 + 12.5) | 1.20 | Per sheet |
| 52.5mm (40 + 12.5) | 1.85 | Per sheet |
| 62.5mm (50 + 12.5) | 2.30 | Per sheet |
| 77.5mm (65 + 12.5) | 3.00 | Per sheet |
Thinner wall or single sheets?
K118's lower λ means it reaches a given R-value with less insulation. At 62.5mm overall, K118 gives R 2.60 m²K/W against PL4000's 2.30 m²K/W. To get about R 3.0, PL4000 needs the 77.5mm board (R 3.00), while K118 reaches R 3.15 at 72.5mm. In a small room insulated on two opposite walls, those millimetres add up.
PL4000 is sold by the single sheet, which suits small jobs and part-rooms. K118 comes in full packs only, which suits whole rooms and larger projects.
Which should you choose?
- Kingspan K118: the thinnest wall for a given R-value, when floor space matters or you need to reach a tight U-value target.
- Celotex PL4000: a PIR board bought by the sheet, for smaller jobs or where a slightly thicker lining is acceptable.
Whichever you choose, ask the manufacturer or a designer for a U-value and condensation risk calculation for your wall. For fitting, see how to install insulated plasterboard and how to fit insulated plasterboard to a solid wall.
Delivery
We deliver to England only.
- Celotex (Sopratherm): minimum order £250 ex VAT; delivery is £40 ex VAT on Celotex orders under £550 ex VAT and free from £550 ex VAT.
- Kingspan, Recticel and other PIR boards: free delivery, minimum order £400 ex VAT.
Need help choosing or working out quantities? Call us on 03330 908479.