Project Overview

The Project – Window Inserts

Molygran specialises in the profile cutting of expanded polystyrene. By creating window inserts inside frames this provides a polystyrene thermal barriers.  Using these inserts within aluminium structures is common. However, they are now increasingly common within PVC-U structures. Installing profile cut polystyrene thermal barrier inserts insulates voids as well as preventing cold bridging.

As regulations for thermal insulation tighten on all building works, prevention of cold bridging is becoming increasingly important for manufacturers of window sections and polystyrene thermal barriers (or thermal breaks) are certainly a necessary addition to the windows design and specification.

We only manufacture from the highest quality expanded polystyrene. Molygran’s specialty is cutting profiled insulation inserts custom made to fit any window section. Our expertise and state of the art machinery enables us to manufacture to the exacting standards. Therefore, we are able to produce the most intricate work. Made from 98% air, expanded polystyrene as a result it has fantastic insulative qualities. Expanded polystyrene is a low thermal conductor which will help prevent heat loss through the window sections.

For More Information – Contact Us


window inserts
roof insulation


  • Polystyrene is a low thermal conductor and will prevent heat loss through window sections
  • EPS inserts are easy to install as they are cut to fit snuggly in the section
  • Polystyrene is environmentally friendly- no toxic substances are used during the manufacturing of EPS
  • Molygran have over 130 years experience and can work to your exacting standards
  • Molygran's procedures allow for integration with our customers "just in time" systems
  • Molygran have no tooling costs meaning a wide range of insert shapes is possible

The brief The brief

2018 has brought in new legislation regarding the thermal performance of buildings, where the minimum energy performance standard has been raised under the Energy Act 2011. All commercial buildings are now affected by these legislations and Building Regulations for all domestic new builds also require an improvement on the U-values achieved (you can read more about this here.)

With this, there has also been an increase in the prevention of cold bridging and details around windows and doors has taken on greater significance when looking to improve the thermal efficiency of a building.

A cold bridge is an area in a building where a “gap” occurs in the insulation such as the roof/wall junction, window/wall junction and the wall/floor junction. Cold bridges can also be found within the window sections themselves as can be seen in the diagram above. The voids within a window section are filled with a polystyrene core which is cut to fit snuggly within the void to help prevent heat loss.

Manufacturers are now beginning to improve the thermal efficiency by using polystyrene inserts to prevent cold bridging within their window sections.

The solution The solution

EPS offers the best cost-performance ratio of any insulation type and thermal conductivity from as low as 0.030W/mK, therefore using polystyrene to prevent cold bridging within window frames has become one of the preferred methods. Made from 98% air, expanded polystyrene is a very good insulator as heat energy can’t flow through it. Carbon or graphite finished EPS also has additional insulative properties and is often used for insulating purposes.

Polystyrene thermal barriers are being increasingly specified within window design to improve their overall thermal performance. A thermal barrier (or thermal break) is a material with low thermal conductivity placed in a window section to reduce or prevent the flow of thermal energy between the conductive materials of the frame itself.

Here at Molygran, using state of the art technology and the expertise of our staff, we are able to produce polystyrene thermal barriers to fit snuggly into any section. We are able to achieve the most intricate and complicated shapes. With no tooling charges, no requirement for specialist equipment for installation and extremely quick turnaround times, Molygran is an extremely flexible and reactive company.