Insulation collar - BDX Insulates around the roof window frame, reducing heat loss and eliminating cold bridges. Makes insulating and installing the window a simple process. Click fittings ensure a fast and accurate assembly. Comes with an underfelt collar - BFX. Underfelt collar - BFX Ensures a weather-tight seal between the roof window and the roof. Pleated material ensures a flexible and tight seal to the underfelt of the roof, whatever it's construction. Made from diffusion open material to minimise the risk of condensation. Comes with transverse drainage gutter to lead water away from the head of the window if a tile or slate is broken above the window. Welded corners ensure a watertight and simple installation.