All Rationel composite windows and doors consist of at least 90% “heartwood” is on all exterior faces. Heartwood from the centre of slow grown trees is very durable. There are moves to increase it’s usage to all parts of the frame.
All timber is treated in accordance with System ECO2. It is a “eco-friendly” water based 3-layer system. Finger jointed “Engineered” Timber as seen here uses the better parts of the timber, this creates more stable, more durable windows and doors that are free from blemishes and knots and more resistant to movement.