Specify Size & Construction
How to Specify a Large Poly Bag: Width, Gusset, Length and Thickness
A practical guide for procurement managers and packaging engineers on specifying large poly bags correctly. Covers lay-flat width, gusset depth, bag length, and thickness measurement.
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Prepare width, gusset, length and thickness inputs that a supplier can review without guessing the measurement convention.
When you request a quote for large poly bags, the supplier needs four key measurements to give you an accurate price and to confirm whether their equipment can produce your bag. Getting these dimensions right the first time saves days of back-and-forth emails.
1. Lay-Flat Width
The lay-flat width is the width of the bag measured when it is laid completely flat. For a bag without gussets, this is simply half the circumference of the bag opening.
To determine the width you need:
- Measure the widest point of your product.
- Add 50–100mm on each side for easy insertion.
- For irregular shapes, measure the largest cross-section.
If your product is 1400mm wide, you might specify a bag with 1600mm lay-flat width.
2. Side Gusset Depth
A side gusset expands the bag's internal volume without increasing the lay-flat width. This is especially important for thick products like mattresses and furniture cushions.
Gusset is expressed as 2 × depth (e.g., 2 × 250mm means each gusset fold adds 250mm of depth on both sides).
To choose gusset depth:
- Measure your product's thickness.
- Add 20–50mm for ease of loading.
- The total gusset should accommodate the full product thickness.
For a mattress that is 300mm thick, a gusset of 2 × 250mm or 2 × 300mm would be appropriate.
3. Bag Length
Bag length is the distance from the bag opening to the bottom seal. For side-gusset bags, measure from the top opening to the sealed bottom.
To determine length:
- Measure your product's longest dimension.
- Add 100–200mm for sealing or folding over the top.
- Consider whether the bag needs extra length for vacuum sealing or taping.
4. Thickness
Thickness is typically specified in microns (μm) or mil (1 mil = 25.4μm). For large industrial bags, thickness is measured on a single layer.
Illustrative discussion ranges sometimes used for initial review are:
- 40–60μm: Light-duty dust covers and inner liners
- 60–80μm: Standard mattress and furniture bags
- 80–120μm: Heavy-duty bags for sharp or heavy products
These ranges do not define a universal performance grade. Resin, film structure, corners, handling and test conditions all affect the result. State the target thickness and the tolerance your control plan requires; a ±10% tolerance is an example used in one sanitized record, not the default for every order.
Putting It All Together
An example specification for discussion looks like this:
Product: Large-Size LDPE Mattress Bag
Lay-flat width: 1600mm
Side gusset: 2 × 250mm
Length: 2200mm
Thickness: 70μm (±10%)
Material: LDPE/LLDPE blend, clear
Closure: Bottom seal, open topThe numbers above are an example, not a universal mattress-bag construction. Send the packed-product dimensions, measurement convention and loading method so feasibility, allowance and tolerance can be reviewed before quotation.