Reflective insulating crown board 8mm Polynum®

01 · WHERE THE HEAT GOES

Under a metal roof, heat leaves by radiation

Heat escapes a hive three ways: conduction through the walls, convection through air currents and radiation. The metal roof is the weak point in all three — in winter it radiates the cluster's heat out to the night sky, and in summer the reverse, it heats in the sun and sends that back down. A reflective material does not fight this with thickness: it fights it with low emissivity. The aluminium on both faces returns radiation the way it came, and the polyethylene bubble in between breaks the conduction bridge between the two skins. That is why 8 mm of reflective sheet and 8 mm of foam are not comparable: they address different loss paths.

02 · WHERE IT GOES

The closer to the cluster, the better it works

The usual place is directly on the frames, instead of the cloth quilt or the sheet of newspaper. It also sits on the crown board, and if you are feeding it goes above the feeder, never below: the sheet must not block access to the syrup. Inside it performs better than on top of the roof, but if you fix it to the metal roof leave an air gap between sheet and metal — a reflector pressed against the hot surface conducts instead of reflecting, and loses half its point.

03 · HOW IT BEHAVES IN THE HIVE

They propolise it, they don't chew it, and it takes no moisture

Against cloth or paper it has an advantage you notice by the second winter: it absorbs no moisture — no mineral fibre, no cellulose — and does not mat down, so it neither loses properties nor grows mould. Bees propolise the edges but do not chew it, and the material holds up. That said: it is a thin sheet and it can tear if you yank it when well propolised — lift it with the hive tool from one edge, like any crown board. And it comes sized to the opening, 500 × 430 mm: it sits flush, it does not overlap the box rims.

04 · BEFORE YOU BUY

The factory size fits the opening of Langstroth and Dadant hives and Nicot-type plastic covers. For any other format — Layens, home-built hives, shallow supers — cut it with scissors: measure your internal opening and compare it with the sheet's 500 × 430 mm before ordering. Sold by the unit, not by the roll.