How to Specify Bespoke Polythene Bags and Sacks for Industrial Use
Bespoke polythene bags and sacks can look like a simple packaging purchase, but small specification choices affect protection, packing speed, material use and cost. A bag that is too narrow can be slow to load. Excess length adds material without adding protection. The wrong seal or film thickness can create failures during filling, storage or transport.
For engineering components, manufactured goods, warehouse stock, contract-packed products and distribution applications, the most reliable starting point is the complete packing process—not a nominal bag size copied from an old order.
This guide explains the information that helps us recommend a practical, repeatable specification.
Start with the product and its journey
Before choosing dimensions or film thickness, describe what the bag must contain and what happens after filling. Useful details include:
the product’s size, shape and weight;
whether edges, corners or protrusions could stress the film;
whether the contents are loose, boxed, stacked or pre-assembled;
how the bag is filled, closed and handled;
the storage period and conditions; and
whether packs travel individually, in cartons, in totes or on pallets.
A bag used as a clean dust cover has a different job from a heavy-duty sack carrying loose components. Understanding the journey prevents unnecessary material being added in one area while a genuine risk is overlooked elsewhere.
Choose the right bag or sack format
A straightforward flat bag can suit regular items and general containment. Bottom-weld construction provides a clear base seam and is widely used for industrial, storage and distribution applications. Bags can also be supplied perforated on a roll where this improves dispensing and workstation organisation.
Side or bottom gussets give the pack additional depth and can help film sit more naturally around bulky, square or irregular contents. The gusset should be sized for the actual filled profile: too little restricts loading, while too much can create loose film and inefficient material use.
For larger loads, components or robust warehouse handling, a heavier sack specification may be appropriate. “Heavy duty”, however, is not a complete technical specification. Load weight, sharpness, drop height, closure method and handling conditions still need to be defined.
Calculate finished dimensions from the filled pack
Product width and height alone rarely produce the correct bag size. Allowance is needed for depth, loading clearance and closure. For a flat bag, the required width is influenced by the product’s width and depth. The length must accommodate the product, its depth and enough film for the chosen seal, tie or fold-over closure. Gusseted formats distribute that allowance differently.
The most dependable approach is to provide a product sample, filled-pack dimensions, an existing bag or a simple drawing. We can then help establish a trial size. This is especially useful for irregular components and assemblies, where a small dimensional change can make a noticeable difference to packing speed.
Specify film thickness by performance, not habit
Film thickness is commonly expressed in microns, but micron alone does not predict how a pack will behave. Polymer blend, film structure, seal quality and the way forces are applied all matter.
the total filled weight;
puncture and tear risks;
whether bags are dragged, dropped or tightly stacked;
the temperature during packing and storage;
how many times the pack is handled; and
whether clarity, stiffness or flexibility is important.
Increasing gauge can add strength, but simply ordering a thicker film may add cost and plastic without fixing a poorly sized bag, a vulnerable seal or a handling problem. A controlled trial is a better basis for approval than gauge alone.
Match the seal and closure to the operation
The factory seal must remain consistent under the intended load. The customer-applied closure must also suit the line. Some operations heat-seal the open end. Others use ties, tape, clips or a fold-over closure before placing the bag in an outer container. Each method needs sufficient spare length and a practical presentation at the packing station.
If the pack is heat-sealed, share the sealer type, seal-bar width, operating temperature range and target cycle time. If operators load manually, assess whether the bag opens easily and whether its presentation reduces unnecessary handling.
Consider colour, print and identification
Clear film supports visual inspection and product identification. Coloured or tinted film can help segregate product families, identify waste streams or distinguish work-in-progress from finished stock.
Printing can add handling instructions, product information, batch or traceability fields, recycling information and branding. Artwork, print position, number of colours and required print repeat should be agreed alongside the bag dimensions so that information appears in the correct place on the filled pack.
Decide how bags should be presented to the line
Packaging performance includes the way bags reach the operator. Loose-packed bags may suit one process; perforated bags on a roll may provide better control and quicker dispensing in another. Pack quantity, roll weight, core size, perforation strength and workstation space can all affect usability.
For contract packing or multiple production sites, a clear specification and agreed presentation help create consistency between operators, lines and locations.
Review recycled content in the complete specification
Post-consumer recycled (PCR) content can reduce reliance on virgin polymer and may be suitable for many industrial bags and sacks. The right percentage depends on performance, appearance and any regulatory or product-contact requirements.
As of 1 April 2026, UK Plastic Packaging Tax is charged at £228.82 per tonne on relevant finished plastic packaging components containing less than 30% recycled plastic. Scope, exemptions, registration thresholds and record-keeping still need to be considered for each business and application.
Rather than adding recycled content as an isolated purchasing target, assess it alongside gauge, bag dimensions, seal performance and real-world trials. The best result is a specification that uses material efficiently and still protects the product throughout its journey.
Approve the bag against measurable criteria
A sample or line trial should reproduce normal packing conditions. Agree what success looks like before the trial, such as:
easy and repeatable loading;
no punctures or splits during handling;
seals remaining intact under the intended load;
acceptable pack appearance and clarity;
reliable dispensing from the roll or pack; and
no unnecessary film in the finished pack.
Record the approved dimensions, gauge, material blend, colour, print, seal construction and presentation. This turns a bag description into a controlled packaging specification that can be repeated on future orders.
A practical specification starts with the application
Stretchband Packaging supplies bespoke POR bags and bottom-weld sacks for manufacturing, processing, logistics, distribution and contract-packing applications. If you are reviewing an existing pack or developing a new one, send us the product dimensions, filled weight, current bag details and a short description of the packing process. We can help identify a sensible starting specification and arrange samples or trials where appropriate—without pressure to change a specification that is already working well.
