108mm Pipe Insulation

108mm pipe insulation fits steel pipe with a 108mm outside diameter — equivalent to 4 inch nominal bore steel pipe, widely used for large commercial heating mains, chilled water distribution, district heating and industrial process pipework. We stock a full range of 108mm pipe insulation from the UK's leading manufacturers including Armaflex, K-Flex, Rockwool and Kingspan Kooltherm, in wall thicknesses from 25mm to 60mm.

Types of 108mm Pipe Insulation

Armaflex EVO 108mm — Class O closed-cell nitrile rubber foam with built-in vapour barrier. Available in 25mm wall, standard and self-seal. The professional's choice for chilled water and HVAC applications at this pipe size
K-Flex ST 108mm — Class O elastomeric foam, equivalent performance to Armaflex at a competitive price. Available in 25mm wall
Rockwool Rocklap 108mm — A1 non-combustible mineral wool with foil facing for high-temperature applications up to 750°C. Available in 25mm, 40mm, 50mm and 60mm wall. The specified choice for steam mains and high-temperature heating at this pipe size
Kingspan Kooltherm 108mm — Premium phenolic foam (λ = 0.021 W/mK). Thinner walls achieve the same Part L performance as thicker elastomeric or mineral wool insulation — ideal for space-constrained plant rooms and risers

Which Wall Thickness Do I Need?

25mm wall — Standard for commercial HVAC, chilled water and heating mains at this pipe size. Meets Part L and CIBSE Guide C for most commercial applications
30–40mm wall — Enhanced performance for district heating, exposed pipework and high-performance specifications
50–60mm wall — High-temperature heating mains, steam and industrial process pipework (Rockwool)

BS 5422 for 108mm Pipe Insulation

For LTHW commercial heating on 108mm OD pipework, BS 5422 requires a minimum of 30mm Kooltherm or 32mm Armaflex EVO. For steam and high-temperature applications, Rockwool Rocklap is the correct specification. Read our full guide: BS 5422 Pipe Insulation Standards Guide.

108mm Pipe Insulation — Common Applications

Large commercial heating mains (4 inch steel pipework)
Chilled water mains in large commercial and industrial HVAC systems
District heating and heat network primary mains
Steam distribution and condensate return pipework
Industrial process and cooling system pipework
Data centre chilled water infrastructure

How to Measure Pipe Insulation

Pipe insulation is sized by the outside diameter (OD) of the pipe. For steel pipe, 108mm refers to 108.0mm OD (4 inch nominal bore). Always measure the outside of the pipe before ordering — steel pipe OD differs from nominal bore size.