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K‑FLEX® ST – Euroclass B1‑s2,d0 Pipe Insulation

K‑FLEX® ST is a flexible closed‑cell elastomeric insulation offering low thermal conductivity, high vapour resistance and reliable fire performance for HVAC, refrigeration and heating applications.

Euroclass B1‑s2,d0 Fire Rating0.033 W/m·K λ at 0°Cμ ≥ 10,000 Vapour ResistanceClosed‑Cell Elastomeric Foam

K Flex ST Nitrile Rubber Insulation Product Range

9mm Wall Thick K Flex

9mm Wall K Flex Euroclass B Nitrile Rubber Pipe Insulation

13mm Wall Thick K Flex

13mm Wall K Flex Euroclass B Nitrile Rubber Pipe Insulation

19mm Wall Thick K Flex

19mm Wall K Flex Euroclass B Nitrile Rubber Pipe Insulation

25mm Wall Thick K Flex

25mm Wall K Flex Euroclass B Nitrile Rubber Pipe Insulation

32mm Wall Thick K Flex

32mm Wall K Flex Euroclass B Nitrile Rubber Pipe Insulation

K Flex Rolled Sheet

K Flex Rolled Sheet Euroclass B Nitrile Rubber Pipe Insulation

K Flex Accessories

Accessories for use with K Flex Pipe Insulation

For a full range of pipe insulation lagging we have available,

see our Pipe Lagging & Pipe Insulation category.

K-Flex ST/SK Benefits

Performance Benefits


  • Euroclass B-s2,d0 fire rating for enhanced safety and compliance across HVAC, heating and hot water systems.
  • Closed-cell elastomeric structure provides a built-in vapour barrier, reducing the risk of condensation on low-temperature pipework.
  • Low thermal conductivity (as low as 0.033 W/m·K at 0°C) helps minimise heat loss and improve system efficiency.
  • High emissivity surface supports effective condensation control, particularly on chilled water and refrigeration lines.
  • Resistant to mould, fungi and bacteria due to its material formulation, making it suitable for hygienic environments.
  • Supports BS 5422:2023 and Part L compliance when installed at the correct thickness.


Practical Benefits


  • Self-seal (SK) design allows fast, clean installation of pipe lagging without additional adhesives.
  • Flexible and lightweight, making it easy to work with in tight plantrooms and retrofit applications.
  • Pre-split tubes simplify installation on existing pipework and reduce labour time.
  • Durable and impact-resistant, suitable for both domestic and industrial environments.
  • Consistent finish thanks to the factory-applied adhesive closure, improving appearance and performance.
  • Wide application range including refrigeration, air-conditioning, heating, plumbing, tanks and fittings.

K-Flex ST/SK Technical Specification

PropertyValue
MaterialClosed-cell elastomeric nitrile rubber insulation
Thermal Conductivity (EN ISO 8497) ≤25mm: 0.033 W/m·K at 0°C
>25mm: 0.036 W/m·K at 0°C
0.037–0.038 W/m·K at 40°C
Temperature Range (EN 14707)-40°C to +85°C
Fire Performance (EN 13501-1)Euroclass B-s2,d0
Water Vapour ResistanceHigh vapour resistance due to closed-cell structure
Surface EmissivityHigh-emissivity surface suitable for condensation control
Biological ResistanceResistant to mould, fungi and bacteria
FormatPre-split tubes with factory-applied self-seal (SK) adhesive
ApplicationsHVAC, chilled water, refrigeration, heating, plumbing, tanks and fittings
ComplianceSupports BS 5422:2023 and Part L when installed at correct thickness

Frequently Asked Questions

What is K-Flex ST/SK pipe insulation?+

K-Flex ST/SK is a Euroclass B-s2,d0 closed-cell nitrile rubber pipe insulation designed for HVAC, heating, hot water, refrigeration and chilled water systems. It features a flexible elastomeric core and a factory-applied self-seal (SK) adhesive for fast installation.

Is K-Flex suitable for condensation control?+

Yes. K-Flex has a high-emissivity surface and a closed-cell structure, making it ideal for preventing condensation on low-temperature and chilled pipework. Correct sealing of seams and joints is essential to maintain the vapour barrier.

Does K-Flex meet BS 5422:2023 requirements?+

Yes. When installed at the correct thickness, K-Flex ST/SK can be used to meet the insulation requirements of BS 5422:2023 and Part L of the Building Regulations. Thickness tables for domestic heating and hot water are included on this page.

What fire rating does K-Flex ST/SK have?+

K-Flex ST/SK is classified as Euroclass B-s2,d0 under EN 13501-1, making it suitable for a wide range of commercial and domestic applications where enhanced fire performance is required.

Is K-Flex resistant to mould and bacteria?+

Yes. Due to its elastomeric formulation, K-Flex is resistant to mould, fungi and bacteria, making it suitable for hygienic environments such as food production, healthcare and pharmaceutical facilities.

What temperature range can K-Flex be used in?+

K-Flex ST/SK can be used between -40°C and +85°C, covering chilled water, refrigeration, heating and hot water applications.

Is K-Flex easy to install?+

Yes. The tubes are pre-split and include a self-seal adhesive strip, allowing quick installation on new or existing pipework. The material is flexible and lightweight, making it easy to work with in tight spaces and retrofit projects.

What pipe sizes and thicknesses are available?+

K-Flex ST/SK is available in all common pipe sizes and wall thicknesses including 9 mm, 13 mm, 19 mm, 25 mm and 32 mm. Rolled sheet and accessories are also available for tanks, vessels and fittings.