Understanding Fabric Weights

The Importance of Understanding Fabric Weight

One of the most important aspects of supplying the proper FIBC for an application is determining correct fabric weight for the body panels of the bag. The proper fabric weight is essential to the performance and safety of the FIBC while insufficient fabric weight could lead to tearing, sifting or leaking, catastrophic failures, and potential injury to employees handling the bags.

In general, bags are manufactured the match the correct fabric weight with the specified safe working load and safe factor (4:1, 5:1, or 6:1) to maintain a cost-effective bag that will meet the SWL and test standard to support the load – this would be considered a “performance rated” bulk bag.

However, it’s not always that simple. Most customers understand that heavier fabric weights can handle more stress and higher weight loads. However, heavier fabric may be needed for other packaging issues. Here are a few examples:

Sifting Purposes

Heavier fabric may be required for sifting purposes as the thicker fabric will stretch less under load, which reduces the likelihood of voids in the material for the product to sift from.

Loading Temperatures

Heavier fabric may be used for products with higher loading temperatures to ensure that the fabric does not melt and lose its integrity.

Sharp-edged Products

Heavier fabrics may be needed if the product being packaged has sharp edges increasing the threat or punctures.

Peace of Mind

Heavier fabric may be needed for a customer’s piece of mind knowing that an “over-specified” bag produces less safety risks in their operation.

Fabric weights vary based on the application, product being packaged, and the customer’s requirements. Tape thickness can be adjusted up or down to increase or decrease the fabric’s weight. For bags that are laminated or coated, the coating typically weighs 30gsm. The following chart is a basic guide for matching the fabric required to meet common SWL.

Safe Working Load Fabric Weight
2000lbs 5.0oz / 150gsm
2500lbs 5.5oz / 180gsm
3000lbs 6.0oz / 200gsm
3500lbs 6.5oz / 225gsm
4000lbs 7.0oz / 250gsm

Fabric weight for Tubular Bags vs U-Panel or 4-Panel Bags

For tubular bags, the body of the fabric will have an equal fabric-weight on all 4 sides of the bag. Depending on the specified SWL and application, the manufacturer may choose to include a reinforcement area at the loop attachment points to provide additional support for the body of the bag when the filled bag is suspended via the loops. This reinforcement area is generally 30gsm higher than the rest of the body fabric and is comprised of heavier weft tapes woven into that portion of the fabric.

For U-Panel or 4-Panel bags, in most applications, the body panels of all 4 sides are the same fabric weights. However, depending on your application, some manufacturers may choose to produce U-Panel bags with a heavier gsm fabric for the “U” panel and a lighter gsm for the 2 side panels. With the “U” panel carrying much of the load and making up the base, this bag would handle the SWL while reducing the overall gsm of the bag. While not an advisable manufacturing practice, this may be suitable for some applications.

Understanding Fabric gsm vs. oz

All fabrics have a textile weight and it is common in the FIBC industry to see fabric weights listed in both oz and gsm. GSM stands for Grams per Square Meter while OZ stands for Ounces per Square Yard. Fabric GSM or OZ are directly proportional to the thickness of the fabric; As the value of gsm increases, the thickness increases as well. The following conversion chart shows the gsm to oz conversion for some of the most popular fabric weights for FIBCs.

Fabric gsm to oz Conversion Chart
gsm to  oz/yd2 gsm to  oz/yd2
70gsm = 2.0oz 200gsm = 5.90oz
100gsm = 2.95oz 220gsm = 6.49oz
150gsm = 4.42oz 225gsm = 6.64oz
170gsm = 5.01oz 250gsm = 7.37oz
180gsm = 5.31oz 270gsm = 7.96oz
190gsm = 5.60oz 285gsm = 8.44oz


Please follow along next month to learn how to test your fabric weight to ensure it meets your written standards.



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