The slopes are cut from aluminum sheet. The color can be any color you wish. A specialist cuts the sheet, bends the blanks and installs the jambs on the outer part of the frame. Aluminum overlays will protect the opening from rain, snow, sunlight. This is an additional protection for the window structure. Aluminum is rigid, durable, it will not be damaged if the window accidentally hits a branch or other hard object. The slopes also increase the tightness of the window.