Among the many varied features of bulk bags, such as size, style, and fabric, one of the most important is whether the bag is uncoated or coated.

Uncoated bulk bags are made of a standard woven polypropylene fabric that inherently has spaces or voids in the weave which allows for breathability in the woven material. Uncoated bags are commonly used in applications wherein the product being packaged is organic – such as feed, seeds, and grain – and needs to be allowed to breathe to prevent mold or mildew growth. Uncoated bags may also be used in applications in which the bags are being filled under pressure. In this case, the air gaps in the woven material and allows air to escape from the bag as the product is loaded, preventing an airlock during the filling process. Uncoated bags are suitable for products that are coarse or have a large particulate size.

Coated bulk bags are manufactured through a process of lamination in which a thin layer of a polypropylene film is applied to sheets of woven polypropylene fabric. The coating/lamination provides a barrier to protect the contents of the bag from sifting or leaking through the voids in the woven fabric. The lamination also provides a minimum barrier for moisture and protects the products from the environmental conditions and/or contaminates found outside the bag from being introduced into the product. Coated bulk bags are typically used to hold and transport dry, flowable products in powdered form – such as sugar, flour, silica sand, metallurgical products, etc.

For dry products that must stay absolutely dry, such as salt or cement, and require a greater barrier film, an internal poly liner can be added to the woven bag. PE liners can also be used in applications where standard coating and sift proofing are not enough to keep extremely fine products from leaking.

Our FlexSack Bulk Bag Experts have worked with manufacturers and distributors of virtually every type of product carried by bulk bags for more than 25 years. We can accurately specify and supply the exact bag to meet your particular product’s storage and transportation needs.

Discuss your product’s characteristics and storage and shipping needs with a FlexSack Expert by calling 205.620.9889 or emailingSales@FlexSack.com.