Crop drying apparatus comprises a composite outer cover 1 for covering bales or bins of straw, hay, herbage etc and two end panels. The outer cover comprises an impervious/impermeable, translucent outer membrane 2, two impervious non-translucent inner membranes 3 and two impervious tensioning eyelet extensions 4. The inner membranes are joined together with a porous/permeable membrane 15 to form an enclosure within the outer cover for the purpose of heating air. The enclosure is tensioned over the bins or bales with the porous membrane located over the top of the bins or bales. Both ends of the outer cover extend over the end panels to form an air-tight seal. Air in the enclosure is heated by solar energy and passes through and dries the herbage, the moist air being exhausted to the atmosphere from underneath the bins or bales.
