Bulk bags are an extremely versatile bulk packaging option. If the material/product is dry and flowable, you can store or transport in these amazing bulk packaging bags.

All FIBCs are made with woven polypropylene which are constructed by weaving strands of polypropylene together. This weave is what puts the flexible in “Flexible Intermediate Bulk Container” (FIBC). Because of this weaved construction, very fine materials/products may seep through the weave or the sew lines causing a loss of product and creating quite a mess wherever the bag is.

No bag is 100% sift-proof, but there are a few different ways to prevent very fine products from seeping out of bulk bags. Let's determine and explore these different methods of preventing very fine products from sifting through FIBC’s.

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My product is seeping/sifting through my bulk bag. What are my options?

During the manufacturing process, sewing machine needles make small holes in the fabric of the bag. These can cause a leak if the bag is filled with very fine products/materials.

If you have product/material seeping through your bag, you have two options. One options is using a coated bulk bag. It’s the most common and prevents most products/materials from sifting through the bag. For more information on coated bags, see our blog post “How to Choose Between Coated and Uncoated Bulk Bags for Your Application” by clicking here. 

The second option that you have is using bulk bags with sift-proof/sift resistant seams. Inserting a sift-proof/sift-resistant seam into the bag involves using a felt or spongy type yarn in the sewing process. The sewing operator feeds the sift cord along the seam of the bag when sewing, filling the areas near the needle hole in the seam. At times, felt is used as the sift resistant material and is sewn either along the threaded seam or in between the fabric panels.

The most robust sift-proof/sift-resistant seam design available involves one strip of felt between the polypropylene seam with filler cord on the top and bottom of the seam. In most cases, coated bags are the most cost-effective option and work for most products.

FIBC Big Bags with Sift-Proof/Sift-Resistant Seams Use

As stated above, for most granular and some powder materials/products, coated bags are a great option. If your product/material still seeps through a coated bag, a sift-proof/sift-resistant bag is probably best for you. These bags are perfect for hauling products/materials that are very fine powders such as milk powders, iron powders and/or resins.

For more information on sift-proof/sift resistant bags, contact our team of experts by scheduling some time to speak with us or by giving us a call.

Thanks for reading! 

Thanks for reading this post! We hope this helps you determine if a sift-resistant seam is right for your application.

Safety and reliability are our top priorities. Each bag that we sell has a safe working load (SWL). To make sure the product you’re packing will not exceed the SWL of the bag you’re interested in, you’ll need to know the bulk density of the product you’re packing as well as the cubic foot capacity of the bag.

Click the button below to download our Product Weight Guide and FIBC Volume Calculator to help you determine how much weight a specific bag will hold.