Grain bag quality. All storage bags are not made equal. Although some bags are still manufactured using a single thick layer of plastic, today’s industry standard is the three-layer, co-extruded polyethylene tube, and the norm is 9 ft. (2.70 meters) in diameter and 200 ft. (60 meters) in length, capable of holding about 200-220 tons of grain or the equivalent of 3,3-3,7 tons/m. It is important to emphasis the fact that these bags are specifically designed to hold grain, not chopped forage. Although they may look similar, a grain bag must conform to more demanding standards, basically because grain’s higher specific weight and the fact that it flows freely impose a far heavier load on a bag’s sidewalls and underside than forage does.  The outer layer of a grain bag is a bright off-white color to reflect infrared radiation (i.e., heat from the sun) back into the atmosphere, while its inner layer is black in order to help maintain a lower than ambient temperature inside the ba g by acting as a sunlight (i.e., visible light) barrier. Even though polyethylene is the basic material of all grain bags, manufacturers have developed proprietary resin formulations to withstand the rigors that bags are subject to. In a top quality bag the plastic sheet should possess several attributes:

• It must have the prescribed thickness,
• It must be capable of withstanding the pressure exerted by the grain and stretch within the assigned limits without undue deformation,
• It must be airtight to prevent the entrance of oxygen and any gaseous exchange with the atmosphere,
• It must be impervious to water and moisture,
• It must be resistant to mechanical damage and punctures from outside sources such as birds, mites, rats, machinery.
• It must also preserve its resilience and endure aging and material fatigue after many months under the sun, so it is requisite that the plastic resin be formulated with effective ultraviolet ray inhibitors. Thus, it must be able to be used in both cold weather conditions with minus 20-40 degrees and warm conditions, peaking at 40-45 degrees.