Windows frames made from uPVC material are non-conductive and provide best thermal insulation at relatively low cost and are durable and are low maintenance. Aluminium is highly conductive and needs to have thermal insulation (made from plastic) inserted into to increase thermal performance. Aluminium provides strong frames and the possibility to build a very large units. Aluminium allows for more colour options than uPVC. uPVC allows for a different colour on the outside and inside.