Quick Answer
What are custom bulk bags?
Custom bulk bags, also called custom FIBCs, are Flexible Intermediate Bulk Containers built to a buyer’s specific dimensions, fabric weight, liner type, fill and discharge super sack configuration, and branding requirements. They’re ordered when stock bags don’t match the product’s weight, flow characteristics, regulatory requirements, or operational setup.
At FlexSack, we currently manage over 350 active custom specifications across industries. Samples are available before any full order is placed.
Introduction
Most buyers start with a stock bag, and that’s the right instinct.
We stock over 450,000 ready-to-ship FIBCs across 95 SKUs, ranging from 18″ to 75” height and 400 lbs. safe working load up to 4,000 lbs. When one of those specs fits the product, the application, and the discharge equipment, a stock bag can typically ship the same day.
But not every operation is that straightforward. A product with an unusual bulk density might need a non-standard footprint to fill properly. A food-grade application might require certifications that only specific manufacturing facilities can provide. A company distributing through retail channels might need four-color printing on all four sides.
When those gaps appear between what’s in stock and what the application needs, custom bulk bags are the solution.
“Custom” covers more ground than most buyers realize when they first come to us. This guide covers what can actually be specified and where the real decision points are.
What “custom” actually means for FIBCs
Custom doesn’t mean one-off.
In our world, it refers to any bag built to specifications that differ from what’s available as a standard stock item. Those specifications span eight distinct variables.
| What Can Be Customized | Options Available | Common Reason |
|---|---|---|
| Dimensions & capacity | Any size; SWL from 400 to 3,000+ lbs. | Product density doesn't fit standard footprints |
| Bag panel construction | 4-panel, tubular, U-panel, baffle | Stackability, cube efficiency, flow requirements |
| Fabric & coating | Uncoated, coated, various GSM weights | Moisture protection, product sift resistance |
| Liners | PE film, barrier film, aluminum foil | Product sensitivity to moisture, oxygen, vapor |
| Fill & discharge | 4 top options × 4 bottom options | Equipment compatibility, flow control |
| Lifting configuration | 5 loop styles including stevedore and chain | Lifting equipment, load distribution |
| Printing | Up to 4 colors, all 4 sides | Branding, hazard marking, regulatory labeling |
| Certifications | Food-grade, UN/DOT, Type C/D static | Regulatory requirements by product and industry |
Some custom orders touch only one of these. A buyer might need a non-standard dimension with everything else kept at stock specs.
Others involve all of them. A pharmaceutical application might require specific dimensions, a multi-layer barrier liner, full-bottom discharge, and BRCGS-certified manufacturing before the bag even gets to printing.
Understanding which variables matter for your application is where the custom process starts, and it’s something our bulk bag experts work through with every customer before a specification is finalized.
Dimensions and capacity: getting the footprint right
Dimensions are almost always the first thing buyers bring to us, and they have the most direct impact on how the bag performs in the operation.
Our stock range covers 20″×20″ up to 42″×42″ footprints, heights from 18″ to 75″, and safe working loads from 400 to 4,000 lbs, which covers most standard applications. The gaps appear when a product’s bulk density puts it outside standard weight ranges, when discharge equipment has a fixed footprint that doesn’t match what’s in stock, or when stacking requirements demand a specific bag height for pallet efficiency.
Getting dimensions wrong has real downstream consequences. One of our clients came to us after years of dealing with bags that were oversized and under-spec’d for their actual application. The bags couldn’t support a second bag stacked on top, which limited warehouse density and increased shipping costs.
We correctly sized the bag, increased the fabric weight, and reinforced the seams. The result required less than half of the previous storage space, and we saved our customer $4–6 per bag.
Beyond footprint, panel construction shapes how the bag holds its form under load:
- 4-panel bags: four separate side panels sewn together; strong structural rigidity, the most common style for general industrial use
- Tubular bags: woven as a single cylinder; cost-effective for standard applications where cube efficiency isn’t a priority
- U-panel bags: a continuous U-shaped front and bottom panel; combines 4-panel strength with simpler construction
- Baffle bags: internal baffles maintain a square shape under load; maximizes cube efficiency on pallets and in shipping containers
With dimensions and panel construction set, the next decision is what the bag is made of and how that material performs with your specific product.
Fabric, liner, and coating: matching the material to the product
The shell of every standard FIBC is woven polypropylene. What varies is the fabric weight (measured in GSM), whether the fabric is coated, and what liner goes inside.
Those three variables determine how the bag performs with your specific product, and they’re where we spend the most time during the specification conversation.
Fabric weight is the starting point. Heavier GSM fabrics offer more strength and sift resistance. Lighter fabrics reduce cost and empty bag weight, which matters for return shipping. The right GSM comes from the safe working load required and the particle size of the product. Finer products need tighter weaves at higher weights.
Coating is the next decision. Uncoated fabric breathes, which benefits seeds, organic materials, and grains that need airflow. Coated fabric creates a smoother interior surface that resists moisture infiltration and prevents fine particles from sifting through the weave. Most chemical, fertilizer, and food-powder applications require coated fabric.
Liners add a layer of protection inside the bag itself. The options we work with most:
- PE film liners: the most common choice; protects against moisture and contamination for most dry bulk products
- Barrier film liners: for products with strict moisture vapor or oxygen sensitivity requirements
- Aluminum foil liners: creates a vapor-tight seal for highly sensitive materials like pharmaceutical ingredients or catalysts
- Form-fit liners: contoured to the bag shape to prevent liner collapse during discharge
The liner also affects how the product discharges. A mismatch between liner style and discharge configuration causes the liner to block the spout or collapse before the product fully exits. It’s an easy detail to overlook and an immediate problem on the filling line.
Our liner selection guide covers how to match liner type to application.
Fill and discharge: matching the bag to your equipment
Both ends of an FIBC are engineered to match how product moves in and out. The wrong configuration creates real problems on the floor, not theoretical ones.
Getting this right means matching the bag to your specific equipment and your product’s flow characteristics.
Top fill options:
- Open top: fastest fill rate, best for non-dusting products with overhead fill equipment
- Spout top: reduces dust during filling; standard for powders and fine granules
- Duffle top: fabric extends past the bag body and folds to close; used when a tight seal isn’t needed but a flap closure is
- Conical top: tapers inward; used for specific gravity-fed filling setups
Bottom discharge options:
- Flat bottom: works well for free-flowing products; simple construction
- Spout bottom: the most common discharge configuration; gives controlled flow rate for powders and granules
- Conical bottom: tapers to a point to promote complete discharge of difficult-flowing materials
- Full bottom discharge: the entire bottom panel opens; used for maximum flow rate and complete product recovery
This is one of the areas where working through the spec before ordering saves the most rework later. Our bulk bag experts review fill and discharge configuration as part of every custom specification conversation.
Custom printing: branding, compliance, and identification
We can print up to four colors across all four sides of a custom FIBC. In our experience, that capability serves three different purposes depending on the operation.
Branding is the most visible use. Companies distributing through wholesale or retail channels use printed FIBCs to carry their logo, product name, and imagery at the point of sale or delivery. For landscape supply companies or seed companies selling through distributors, the printed bag is often the first thing a buyer sees.
Compliance labeling is required in certain industries. UN/DOT-certified bags for hazardous materials must carry specific markings identifying the bag’s certification, safe working load, and contents. Food-grade bags may require FDA compliance statements. These aren’t optional, they’re part of the regulatory requirement.
Internal identification reduces handling errors and cross-contamination risk when multiple products or varieties are moving through the same facility. In seed handling especially, color-coded bags and printed lot numbers function as compliance tools as much as operational ones.
Printing adds lead time and is one of the harder elements to change after an order is placed. It should be finalized early in the specification process.
Lead times and what to expect from a custom order
Lead times are where custom orders catch buyers off guard more often than anything else. Stock bags typically ship the same day or within 24 hours. Custom orders don’t, and the timeline depends on how many variables are being changed from a standard specification.
| Order Type | What It Covers | Typical Lead Time |
|---|---|---|
| Stock bag | Standard spec, in-warehouse inventory | Same day or within 24 hours |
| Fully custom | Custom dimensions, construction, liner, printing | 110 - 120 days |
| Certified custom | Any of the above + food-grade, UN/DOT, or Type C/D | 120 - 135 days |
One option worth knowing: we offer samples of custom bags before a full order is placed.
For operations running a new product or specifying a bag for the first time, a physical sample in the hands of the production team prevents specification errors that only surface on the filling line. It’s one of the most practical steps in the custom process, and one of the most underused.
Custom lead times also make seasonal planning critical. If your operation needs custom bags for spring production, late fall is when that conversation should start.
Working with FlexSack on custom specifications
In our experience, the specification process determines if a custom order performs the way it should. A bag built to the wrong dimensions, with the wrong liner for the product’s moisture sensitivity, or with a discharge configuration that doesn’t match the equipment, creates problems that only surface once production is running. At this point, point fixing them takes time the operation doesn’t have.
Our bulk bag experts have over 70 years of combined FIBC experience across feed, seed, fertilizer, chemical, pharmaceutical, building materials, plastics, and landscape supply applications. The process starts with a needs assessment where we review your product, equipment, and any regulatory requirements before a specification is written.
From there, we develop the specification, provide a physical sample for review, and for ongoing custom orders, can store your bags at one of our domestic warehouses at no charge with bi-weekly inventory reports, so you always know what’s on hand.
Whether you’re reviewing bag features and configuration options for a first custom run, confirming that your current bags are correctly rated for your actual filled weight, or planning food-grade compliance documentation for FSMA audits, we work through the details before the order goes in.
Browse our stock inventory first if you want to confirm whether a standard spec fits your application. For custom specifications, contact our Bulk Bag Experts at (205) 620-9889 or email Sales@FlexSack.com.
Frequently Asked Questions
Minimum Order Quantity (MOQs) for custom FIBCs vary based on the complexity of the specification. Dimensions, certifications, and printing all affect the minimum. Our Bulk Bag Experts walk through minimums during the initial quoting conversation. For operations where MOQ is a concern, it’s worth confirming whether a stock bag covers the spec first, since stock bags carry no minimum order requirement.
Fully custom bags with non-standard dimensions or specific certifications run 110-120 days. Certified applications can extend to 120-135 days. Our supply chain management team helps customers plan around these windows, so bags are ready before seasonal demand peaks.
Yes. We manufacture custom bags in certified clean room facilities meeting BRC, AIB, ISO 22000, HACCP, and GMP standards. All certifications need to be specified at the start of the custom process, as they affect manufacturing facility selection and add to the overall lead time.
Start with the stock range. Our 95 SKUs cover 400 to 3,000 lbs. SWL across a wide range of sizes, fabrics, and configurations. If your product and equipment are compatible with a standard spec, a stock bag ships the same day with one pallet MOQ’s. Custom becomes necessary when dimensions fall outside the stock range, when the application has regulatory requirements that need specific manufacturing certification, or when printing is required. If you’re not sure, our bulk bag experts can compare your spec against current inventory before any custom order is placed.