Square-Bottom Liner Bags: Uses, Sizing & Comparisons
Choosing square-bottom liner bags for your product
Square-bottom liner bags fit inside box-shaped containers and separate the contents from the outer carton. Their expanded rectangular base follows the container’s internal dimensions, while extra material at the top allows folding, tying or a specified seal. The liner provides containment; the carton supports stacking and handling.
Square-bottom liner bag specifications
Parameter | Specification |
|---|---|
Container fit | Finished width, height and gusset dimensions match the internal dimensions of the outer carton or container. |
Film specification | Film thickness is measured through one wall. The specification identifies the material, thickness and any required food-contact grade. |
Filling and closure | The opening, filling method and top closure follow the packed material and handling process. |
Load and handling | Fill weight, product density and movement within the outer container guide puncture resistance and bottom construction. |
Order quantity | Unprinted liners are quoted by size, film specification and quantity. Gravure-printed film uses a 6,000 linear metre starting MOQ. |
Quotation | Itemized quotation within 24 business hours. |
Specify a liner for your container
Structure and filled-pack checks
An expanded rectangular base and side dimensions are matched to the inside of the container. The top normally needs enough extra material for folding, tying or a separately specified seal. Measure the container internally and account for corners, insertion and closure instead of ordering solely from external carton dimensions.
Construction details
Use the details below to review the drawing, filling process and filled sample.
1. Container fit
Check the liner inside the actual container. Match the opened base and side dimensions to the carton, tray or tote. Check corner fit, product loading and film stress using the intended container.
2. Top overhang
Allow extra liner height for folding, tying or heat sealing. Set the closing method and top overhang before finalising the dimensions.
3. Contact and handling
Check the product and container edges for abrasion and puncture, and provide support at the base and corners. Specify food-contact materials for the contents and use conditions.
Common applications
Bulk dry ingredients
A liner separates ingredients from the carton and helps keep handling clean. Specify the food-contact film and supporting documents for the product and conditions.
Industrial components or powders
Liners keep contents together and separate them from the box. Specify abrasion, sharp-edge, dust and chemical protection, including any required antistatic or hazardous-material features.
Container lining during packing
Correctly sized liners fit neatly into the container and fold over its rim. Allow operator and filling-equipment access, with enough clearance to keep excess film out of the closure.
Advantages
Container-matched shape
The expanded base can fit a rectangular cavity more naturally than an unsuitable narrow flat bag.
Separate protection layer
The liner and outer container can perform different jobs: containment versus stacking and crush resistance.
Closure flexibility
The open top can be folded, tied or sealed to suit the validated application.
Practical considerations
Container support
Use the outer container for lifting and load support. Lifting by the liner requires a liner system designed and verified for that load.
Closure determines containment
Specify both the film barrier and a suitable sealed closure when moisture or oxygen protection is required. Folding or tying an open-top liner does not create a hermetic barrier pack.
Fit and puncture risks
Oversizing can bunch film into folds; undersizing can stretch it across corners. Both can affect filling and protection.
Compare bag types
Compared with flat-bottom bags
Flat-bottom retail pouches provide a printed consumer pack with a defined closure. Square-bottom liners provide the inner containment layer for a supporting carton or container. Read the flat-bottom bags guide.
Compared with three-side-seal bags
Simple containers also use flat liners. Choose dimensions that fit the corners and opening neatly, with practical insertion and filling access. Read the three-side-seal bags guide.
Compared with perforated bags on a roll
Roll dispensing can be a supply option for some liners. Bag shape and supply format are separate choices: specify both container fit and the way operators take each bag. Read the perforated bags on a roll guide.
Specifications for your quote
Provide the specifications you know and mark any open items as "to confirm".
Specification | What to provide or verify |
|---|---|
Internal container dimensions | Provide length, width, depth, rim details and the required top overhang. |
Load and closure | State product, filled weight, support conditions, handling and whether the top is folded, tied or heat-sealed. |
Product and protection | State contents, target fill, storage and distribution. Identify barrier, puncture, chemical or thermal requirements that need verification. |
Material and thickness | Choose the material structure and thickness for the application and agreed trials. |
Artwork and quantity | Provide print files or artwork status, finish, quantity per design and size, destination and required schedule. |
Sampling and documentation | Agree sample type, machine or filling trials, acceptance criteria and relevant supporting documents before order approval. |
Questions before ordering
How do square-bottom liners and retail flat-bottom bags differ?
A square-bottom liner provides containment inside a supporting container. A flat-bottom retail bag provides a sealed, printed consumer pack.
How should a filled liner and carton be lifted?
Lift the carton by its designed lifting points. Use liner lifting only with a system specifically designed and verified for the filled load.
How is recycled-content film selected for a liner?
Use recycled-content film where the contents, contact conditions and applicable requirements permit it, supported by the material specification and documents.
What are the MOQ, sample lead time and production schedule?
For gravure-printed packaging, the MOQ is 6,000 linear metres of printed film. Normal production takes 15 working days for a first order and 10 working days for a repeat order, counted from signing the formal contract. Shipping time is additional. Send your material, dimensions, quantity per design and artwork status so we can confirm the sample plan. For unprinted bags, confirm the MOQ and production schedule with the material and dimensions.
What evidence should be agreed before approval?
Confirm the specification, sample approval, relevant trial results and acceptance criteria. For regulated applications, identify the market, intended use, document issuer and scope.
Prepare your packaging request
Send the product, target fill, storage or shipping conditions, filling method, quantity per design and destination. Include a sample or drawing if available. Configure square-bottom liner bags and request a quote.
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