Abstract: A passive-type solar device comprising a transparent plate disposed for exposure to sunlight, a reflecting film curtain provided in alignment with said transparent plate and adapted for covering and uncovering movement with respect thereto, and a heat insulating, sunlight transmissible, board provided in alignment with said reflecting film curtain, said board comprising at least first and second sections of predetermined thickness in spaced apart relationship with an intervening air layer, each of said sections being constituted of a honeycomb material member sandwiched between transparent plates.