The invention relates to a folded bag and a method for forming a bag from a square or rectangular shaped sheet, which method comprises the steps of dividing the sheet into nine fields arranged such that eight fields surround a central field; folding the sheet along folding-lines between and across the fields in such a way that the central field forms the bottom of the bag and the eight surrounding fields form the sides of the bag and at least one inner wall providing separated compartments in the bag.