The role of pelmets or an equivalent structure is often overlooked in effective window coverings. Having a physical block or seal at the top of curtains prevents or slows convection currents establishing in the room. As the air behind a curtain cools as the heat passes through the window, the sair will sink, usually to floor level (opposite to hot air rising). Air is pulled in to replace this air, and usually the easiest route is from the top of the curtain. Unfortunately this is also the warmest air in the room (hot air rising again). Convection currents can strip a room of its heat adding significantly to heating costs. Pelmets block or slow the drawing of the warmest air behind the curtain.
Coreflute or fluteboard can be purchased from Bunnings (600 x 900mm boards) or in larger sheets from plastic manufacturer such as Associated Plastics Tasmania.