How to Choose the Right Polythene Bag Thickness

Polythene bags are available in several thicknesses, from lightweight bags for simple presentation and storage to heavier options for industrial components and demanding handling.

Choosing the correct thickness helps protect the contents without using more material than the job requires. The decision should be based on the product’s weight, shape and surface rather than its size alone.

Martins Mill Packaging supplies polythene bags and sacks in light, medium and heavy-duty grades, alongside grip-seal bags, rubble sacks, bin liners and compactor sacks.

What Does Polythene Bag Gauge Mean?

Polythene thickness may be stated in gauge or microns. A higher number indicates a thicker material.

To convert the gauge measurement used for these bags into microns, divide it by four. For example, a 400-gauge bag has a thickness of approximately 100 microns.

Grade	Gauge	Approximate Thickness
Light duty	100g	25 microns
Light duty	120g	30 microns
Medium duty	200g	50 microns
Medium duty	250g	62.5 microns
Heavy duty	400g	100 microns
Heavy duty	500g	125 microns

Gauge describes the material thickness, not a guaranteed carrying capacity. Bag dimensions, seams, contents and handling method will also affect performance.

Light-Duty Polythene Bags

Light-duty bags in 100g and 120g material are suitable for smooth, lightweight products that do not place significant pressure on the film.

Typical uses include:

• Clothing and textiles
• Books, stationery and printed materials
• Small accessories
• Toys and lightweight retail products
• Inner bagging within cardboard boxes
• Keeping clean products free from warehouse dust

The transparent material allows the contents to remain visible, which can help with retail presentation, stock identification and order picking.

Light-duty bags are not intended for sharp, abrasive or particularly dense items. Even a small steel component may require a heavier bag because its edges and concentrated weight can stretch or puncture thin film.

Medium-Duty Polythene Bags

Medium-duty bags in 200g and 250g material provide a step up in strength for everyday commercial and warehouse packaging.

They may suit:

• Components and spare parts
• Moderately heavy retail products
• Warehouse picking and packing
• Textiles and soft furnishings
• Instruction packs and product accessories
• Products requiring a more durable inner bag

Medium-duty film can be a practical starting point where a light-duty bag feels too thin but the contents do not justify the heaviest available grade.

The shape of the item remains important. Smooth products spread their weight across the bag, while narrow corners and projections create pressure in a smaller area.

Heavy-Duty Polythene Bags

Heavy-duty bags in 400g and 500g material are intended for heavier products and more demanding handling conditions.

Possible uses include:

• Steel fixings and engineering components
• Tools and hardware
• Machinery parts
• Heavier warehouse products
• Furniture and larger items during storage
• Industrial inner packaging

Thicker polythene provides greater resistance to stretching and everyday wear, but it is not puncture-proof. Exposed blades, nails, jagged metal and other dangerous items may require edge protection or a rigid container.

Do not assume that a 500g bag is always necessary for a large product. A bulky but lightweight textile item may place less strain on the film than a much smaller box of metal parts.

Choose According to Weight and Shape

Consider both the total weight and how that weight is distributed.

Ask the following questions:

• Does the product have sharp corners or protruding parts?
• Will several items press against one another?
• Will the bag be carried or remain inside a box?
• How many times will it be handled?
• Could the contents move and strike the film?
• Does the bag need to be reopened or reused?

A heavier gauge may be worthwhile when bags pass through several warehouse processes or are handled repeatedly before reaching the customer.

Select the Right Bag Size

Thickness is only one part of the specification. The bag must also provide enough room for the product without being excessively large.

A bag that is too small may be stretched around the contents, placing additional pressure on its sides and opening. An oversized bag uses unnecessary material and may be awkward to seal or arrange inside a box.

Measure the product at its widest and longest points. Where several items will be placed in one bag, measure the complete group in the arrangement that will actually be packed.

Allow enough space to insert and remove the contents without pulling heavily on the seams.

Grip-Seal Bags for Small Products

Where products need to be accessed repeatedly, grip-seal bags may be more practical than an open polythene bag that requires tape, ties or heat sealing.

The current grip-seal range includes plain and write-on-panel bags in 45/50-micron material, plus 70-micron heavy-duty bags.

These are useful for organising:

• Fixings and small components
• Samples and accessories
• Order kits
• Labels and paperwork
• Craft and retail products

The resealable closure makes them convenient for products that need to be counted, inspected or removed in smaller quantities.

When to Use Rubble Sacks or Compactor Sacks

Ordinary clear polythene bags are not designed for every waste application.

Heavy-duty rubble sacks are more appropriate for manageable quantities of building, refurbishment and landscaping waste. Compactor sacks are designed for compatible waste-compaction systems and larger waste-handling tasks.

Select the sack according to the waste type, expected weight and collection method. Hazardous waste, asbestos, chemicals and contaminated materials require an approved specialist container and disposal process.

Are Polythene Bags Waterproof?

Polythene can help protect products from warehouse dust, dirt and light moisture. However, an open or loosely closed bag should not automatically be treated as waterproof or airtight.

The level of protection depends on:

• The thickness and condition of the film
• How the opening is closed
• Whether the bag has been punctured
• The duration and conditions of storage
• Whether water can collect around the package

Products that are highly sensitive to water, humidity or contamination may require sealed specialist packaging.

Check Food and Specialist Applications

The current clear polythene bag listings describe the products as suitable for food use. Businesses must still confirm that the selected bag and packing process suit the exact product and any applicable hygiene or traceability requirements.

Do not assume that a general polythene bag is appropriate for pharmaceutical products, chemicals, hazardous substances or specialist technical applications without confirming its specification.

Use the Lightest Suitable Grade

The most suitable polythene bag is the lightest grade that can safely withstand the product and expected handling process.

Light-duty bags suit smooth and lightweight products, medium-duty bags cover many general warehouse tasks, and 400g or 500g bags provide added durability for heavier or more demanding contents.

For help choosing a size and thickness, contact Martins Mill Packaging with the product dimensions, approximate weight, surface type and intended use.