A solar cover of 457 cm across, from Didak Pool's Solar Pool Cover range. The icon on the packaging says what it belongs to: 'fit round pool', 4.57 m. Along the bottom edge of the box runs the English name, 'floating solar pool cover'.
The material is blue insulating bubble film. According to Didak the air pockets in the film catch the sun and pass that heat on to the water; the box carries a drawing for it, with a sun and arrows through the water surface.
The cover floats by itself and does not have to be fastened. Lay it on the water when nobody is swimming and take it off again before going in. Out of season, store it dry.
Measure your pool before choosing. This size belongs to round pools of 4.57 m; Didak also carries the same cover in 3.05 m, 4.27 m and 4.88 m. The round pool in the packaging photo is there to show what the cover is for and is not part of the delivery.
