The seams of the bulk bag are very important, and not just because they keep the bag together. The bulk bag seams can be sewn to provide a sift proof barrier which helps keep your product in the bag. Picking the right FIBC seams for your product can prevent unwanted discharge from the bag and keep more fine products from escaping, which is called “sift proofing.” This is done by sewing a thick cord, called a filler cord, into the fabric as bag is stitched together. Sift proof seams can be manufactured in a single or double stitch method, and to increase the sift proofing further, felt can be added for extra protection.  

To determine the level or protection you need and what application would need it, we have created this chart to help simplify the details:

 SeamSift Proof LevelUse CasesNo Sift ProofingNoneLarge or coarse products such as rocks, soil, wood chips, soy beans, corn, non-flowable powders OR when a liner is usedSingle Sift Proof

(Single Filler Cord)Minimum Level of Sift ProofingSmaller particle, flowable products such as small seeds, ground products, and sandsDouble Sift Proof (Double Filler Cord)Mid-Level of Sift ProofingFine products, chemicals, mineralsTriple Sift Proof (Double Filler Cord & Felt)Maximum Sift ProofingVery fine powders such as talc, cocoa, and chemicals

NO SIFT PROOFING

(FRONT & BACK)

SINGLE SIFT PROOF

(FRONT & BACK)

DOUBLE SIFT PROOF

(FRONT & BACK)

TRIPLE SIFT PROOF

(FRONT & BACK)

Reach out to our team if you have any questions on sift proofing or want help determining what sift proof level your bulk bags need.