it is necessary that the cloth is well stretched, with a slope of not less than 45°, and that the round bales are placed on pallets (better 2 rows) and not in contact with the ground, haymaking must have been properly dried in the field (20% lower residual humidity). The cloth is not waterproof but hydrophobic (it does not retain water but expels it by gravity or evaporation).

It works in this way: when it rains, part of the water slips on its surface and ends up on the ground, part penetrates into the cloth that holds it and then brings it to the lowest point. In case of heavy and persistent rain, part of the water passes through the cloth, wetting the straw in a variable percentage depending on the intensity of the rain. Being breathable, however, the cloth makes the hay then dry, for this to happen it is important that the hay is stored in a sunny and ventilated position (not close to trees, walls, escarpments, buildings or other heaps). In case of heavy and persistent rains above average there is a risk that the intense humidity blocks the drying.
It is the responsibility of the user to periodically verify the correct installation of the cloth and the correct conservation of the covered material.