Designing a Custom FIBC

June 4, 2021

When designing a custom FIBC, a supplier’s job is to ensure the bulk bag meets the functionality and safety requirements of the customer. Bulk bag specifications can have a wide degree of variability and it’s important that customers understand each component of a bulk bag before they begin the design process. The following information outlines the basic components of an FIBC and answers many common questions new bulk bag users may have. 

Construction: There are 3 basic types of bulk bags: U-Panel, Circular, and Baffled. Circular is also referred to as Tubular. Each bag construction is unique; however, all 3 constructions will perform the same basic function. For more information on bulk bag constructions visit our 4 Loop Bulk Bag Guide

Size: Bulk bag size is written as: Base (1) x Base (2) x Height. Common bag base (platform) sizes are:

35 x 35 – most common U-Panel and Tubular bag base size 

36 x 36 

35 x 41

40 x 40

42 x 42 – most common baffled bag base size 

Bag heights can range from 15” to 96”. 

Southern Packaging Blog Image

Fabric Weight: A bulk bag’s fabric weight (i.e. gauge or thickness) is a critical parameter when designing a custom FIBC. Fabric weight is dictated by the customer’s requirements and the desired Safe Working Load and Safety Factor of the bag. Weight can range from light (ex: 130gsm) to heavy (ex: 240gsm). In general, the higher the fabric weight, the higher the load the bag can support.

Fabric Type: Fabric Types include A, B, C, and D. Types B, C, and D offer different degrees of static protection. For more information on anti-static bulk bags read our guide HERE.

Fabric Color: Most bulk bags are made with white or black fabric. Black fabric is common when packaging products that are dark such as carbon black or humates. However, bag fabric can be made in most common colors including orange, blue and green. Typically, larger minimum order quantities apply when bags are a non-white color. 

Coating: Bag fabric can be coated (laminated) with a thin layer of PP for added moisture protection and sift resistance. Coating does not make the bag waterproof. For more information on Uncoated vs Coated fabric visit our blog post HERE

PE Liner: A bulk bag may come equipped with an internal PE, PP, or foil liner. Liners offer an additional level of product protection and eliminate sifting. They can be loosely inserted or attached inside the bag. For more information on different liner styles visit our Liner page HERE.

Top Style: Top styles include spout, duffle, and full open top. The most common spout top size is 14” Diameter X 18” Length. The diameter and length of a top spout is fully customizable. 

A duffle top acts like a skirt, allowing the bag top to completely open and close. Top spouts, duffles, and discharge spouts are not load bearing. Thus, they are typically made with 3.0oz coated fabric. 

Additional top styles including full open top and top flap are available but are far less common. 

Bottom Style: Bottom styles include flat (no discharge) and discharge spout. The most common discharge spout is 14” Diameter x 18” Length. The diameter and length of a discharge spout is fully customizable. For products that tend to bridge a larger diameter discharge spout is recommended. 

Full bottom discharges are available but are uncommon. 

Closure: A closure with protective flap may be added to the outside of the discharge spout for added protection. Closure types include star (petal) and pajama (iris). Each closure may be equipped with different types of ties. 

Lift Loops: Lift loops are a standard component of all bulk bags. Their length and thickness is customizable. The most common lift loop size is 2”W x 10”L for corner seams bags and 3” x 10” for cross corner loop bags. For more information on lift loops visit our blog post HERE.

lift loop lift loop

A bag may also be equipped with stevedore straps for single point pickup. For more information on stevedore straps visit our blog HERE.

Perimeter Safety Band: A band or belt that is sewn around the top of the bag for added strength.

Lift Loop Color: Like bag fabric, lift loops can be made in various colors. It is not uncommon for bulk bags to have blue or black lift loops. 

Seams: Standard seams will support most product particle sizes. For fine and ultra-fine materials, cording (“filler cord”) can be added to the seams for additional sift resistance. This may also be called dust-proof or double-dust proof seams. 

Safe Working Load (SWL): SWL is the amount of load in pounds or kilograms that a bag is designed to safely carry. Common Safe Working Loads include:

2,000lbs 1,000kg

3,000lbs 1,500kg

4,000lbs 2,000kg

Safe working load requirements are determined by the customer and/or the product being packed. Southern Packaging stocks a wide range of off-the-shelf bulk bags with SWLs ranging from 2,000-4,000lbs. 

Safety Factor (SF): 5:1 and 6:1 – means the bag has passed a top load test at 5X and 6X the bag’s Safe Working Load. 

Document Pouch: Document pouches are customizable in size, orientation, and type. The most common doc pouch is a 10” x 12” Ziplock pouch. 

Printing: Bags can be printed on up to 4 sides. Most manufacturers can print up to 4 colors. Printing capabilities on a bulk bag can be limited due to the nature of the print surface. 

UN Certification: FIBCs can be certified for storing and transporting hazardous materials. UN rated bags undergo tests to ensure their ability to withstand drops, vibrations, and tears. For more information on UN testing procedures visit our blog post HERE

Lead Time: Producing a custom FIBC requires patience. Nearly all bulk bags in use today are made outside the United States. India and China produce the majority of the world’s FIBCs. Lead times range from 10-16 weeks depending on where the bags are produced. For more information on lead time visit our lead time chart HERE


Do you need assistance with a custom FIBC? Southern Packaging, LP has grown to become one of the largest FIBC suppliers in the United States. For more information on custom industrial packaging solutions email us at

Bulk Packaging Terms Made Simple


Let’s Connect