A method for treating a package. In the method a first plastic film sack (14) is provided, that has a flexible wall (18) comprising a plastic film (3), the wall (18) having an outer surface (5). A second plastic film sack is provided. A product of powder form is provided that has an upper size limit which is the particle size smaller than 1 mass-percent of the particles of the product of powder form, which upper size limit is at most 5000 microns and a lower size limit which is the particle size bigger than 1 mass-percent of the particles of the product of powder form. The product of powder form is packed in the first plastic film sack (14), and the first plastic film sack is, at least partly, placed upon the second plastic film sack. According to the invention, such a first plastic film sack is provided in which at least a part of the outer surface (5) of the flexible wall (18), the roughened surface-part (6), comprises antislip protrusions (7) which antislip protrusions (7) are constituted by roughening particles, of polymer material, fixed to the outer surface (5) and the height (8), above the outer surface (5) of the plastic film wall, of at least a part of the antislip protrusions (7) is bigger than the lower size limit of the product of powder form.