Thermal Performance

Thermlock® technology helps keep homes snug and warm
Thermlock® built in

Our unique Thermlock® closed-cell, insulating chamber, hidden away inside every Sheerline window and door act as a thermal break, creating products with class leading thermal performance.

Thermlock® v Polyamide, the difference is clear
Thermlock® v polyamide, the difference is clear
Unique Design

Thermlock® multi-chambered thermal breaks are unique to Sheerline and sit at the heart of every Sheerline product.

Less Conductive

Made from a special high melting point formulation, Thermlock® is almost half as thermally conductive as polyamide.


Thermlock® allows for wider more efficient thermal breaks - meaning every Sheerline product meets the new Part L standards with regular double glazing.

Manufactured to last

Improved screw retention over polyamide helps Sheerline systems pass the most rigorous of tests with ease.

Vertically integrated

Produced in-house, Thermlock® technology brings better performance and with integrated on-site manufacture it also minimises the risk of third-party supply issues.

Keeping homes warm

Cold, crisp lines on the outside hide away our innovative Thermlock® multi-chamber thermal design, helping keep homes well insulated against the worst of the UK weather.

This closed-cell, insulating chambers act as a thermal break, working in conjunction with high performance glazing to create class leading thermal performance, far superior to traditional polyamide thermal breaks.

Outstanding performance

Sheerline's Prestige double glazed windows, with standard high performance glazing have a U-value as low as 1.4 W/(m2K).

While our Prestige windows are as low as 1.0W/(m2K) when specified with triple glazing, also achieving an A+ WER (Window Energy Rating)

Thermal transmittance, also known as a U-value, measures the rate of transfer of heat. The better-insulated a window is, the lower the U-value will be.

Across all components

Sheerline’s cills, ancillaries and corner posts, also feature this same technology coupled with innovative in-built weather sealing that keep draughts and rain safely outside.

No element of the Sheerline system has been overlooked, which helps eliminate any condensation issues caused by cold bridging.

Made in Britain