Also known as multi-layered timber, engineered timber is composed of several layers of timber, with the grains in opposing directions of one another. Wood naturally warps in the direction of the grain when it is affected by moisture. This layering of the timber sections reduces the movement of the timber drastically, as it is evened out over the many layers. This prevents the wood from warping and/or twisting, allowing the windows and doors to open smoothly, year round. This removes the problem that has been suffered with previous generations of timber windows and doors, where the wood can swell or twist, causing the units to stick and become very hard (and in some cases, impossible) to open.
Engineered timber also has greater strength and stiffness than comparable dimensional lumber and is, pound for pound, stronger than steel. It is also a better environmental choice than aluminium or PVC because they have less embodied energy. It also goes without saying that timber windows are head and shoulders above Aluminium and PVC in regards to aesthetics.