Alan Davies presents Best Eco Product award to Richard Kinloch for the unique Hi-Therm sustainability Lintel at the Build It Awards. The Keystone Group is particularly proud of its unique Hi-Therm sustainability Lintel. This product is remarkably 500% more thermally efficient than normal cavity lintels. It has a low thermal conductivity and therefore when used to support the outer leaf in a cavity wall construction it significantly minimises thermal bridging or heat transference.