Abstract: A solar collector is described comprising an extrusion, preferably of cellular plastics material, having a longitudinally extending recess and a metal absorber sheet thereover, a tube disposed within the recess in contact with the metal absorber sheet, and a transparent window. The extrusion recess is of semi-circular cross-section, and the tube is of circular cross-section and has an outer diameter substantially equal to that of the recess. In some described embodiments, the window is received on flanges formed at the edges of the extrusion; and in other described embodiments, it is integrally formed with the plastics extrusion.