The VELUX BDX 2000 Insulation Collar reduces heat loss by insulating around the roof window frame and comes with an underfelt collar which ensures a weather tight seal between the roof window and the roof. The underfelt collar is made from diffusion open material which minimises risk of condensation. It includes a transverse drainage gutter too which leads water away from the head of the window if a tile or slate is broken above the window. Easy installation and comes in a variety of sizes. The BDX 2000 will give you extra protection and peace of mind for a low cost.