Poly bags packaging guide

Poly bags guide

Polybags are among the most practical and popular packaging materials available and are ideal for a massive range of industrial, commercial and retail applications.

We have one of the widest selections you are likely to find online, with everything from light duty 20 micron bags to heavy duty polythene bags capable of holding contents weighing up to 25kg. Clear polythene bags are used for everything from storing nuts, bolts and other small parts to lining cardboard boxes.

They can be quickly and effectively sealed using a range of items such as heat sealers, wire ties and bag sealing tape, so whatever you are using them to store, you can make sure it stays safe and clean at all times.

Poly bags are made from high quality polythene, most of our polybags are also food grade which means that they provide hygienic protection against dust and moisture while at the same time keeping the contents visible.

Why choose polythene for packaging?

Polythene is produced more than any other polymer. It can be processed and reprocessed into many different products.

Polythene products are not biodegradable. Polythene is photo-degradable. It will breakdown in sunlight in about 12 months.

Polyethylene plastic consists of a thermoplastic material and is used in a variety of consumer products.

Polythene is strong, lightweight, water resistant and can endure excessive temperatures.

Polythene has superb moisture resistance and durability make it the ideal choice for industrial packaging supplies.

Low density polyethylene verse high density polyethylene

Low density polyethylene (LDPE) is flexible and soft.

High density polyethylene (HDPE) is crispy and cloudy in appearance.

Poly bag size calculation

Poly bags size calculation
Lining a boxMeasure the width, depth and height of the box to be lined. The depth should be the shorter side. To determine the width (W) of the bag, add 1" to the width of the box. To determine the depth (D) of the bag, add 1" to the depth of the box. The length (L) of the bag is determined by adding the depth plus 1" to the height plus 1". Add another 5" to allow coverage of the box contents.
Round containerMeasure the diameter and height of the container to be lined. To determine the circumference (C) of the container, multiply the diameter by 3.14. To determine the width (W) of the bag, divide the circumference (C) by 2. Add 1" for a looser fit. To determine the length (L) of the bag, add the diameter to the height. Add 5" for overhang.
Square containerMeasure the width, depth and height of the container to be lined. The depth should be the shorter side. To determine the width (W) of the bag, add the width and depth. Add 2" for a looser fit. To determine the length (L) of the bag, add 1/2 the depth to the height. Add 5" for overhang.
Pallet coverMeasure the width, depth and height of the pallet to be covered. The depth should be the shorter side. To determine the width (W) of the cover, add 1" to 2" to the width of the pallet. To determine the depth (D) of the cover, add 1" to 2" to the depth of the pallet. The length (L) of the cover is determined by adding 1/2 the depth to the height.

Poly bag seal types

Seal is term used to describe bottom of a poly bag.

Star seal is a multi-layered seal is full gusseted and then folded prior to sealing, allowing for the weight to be evenly distributed.

Gusset seals is a flat-style bag manufactured with both sides tucked in to form gussets.

Flat seal is a straight seal along bottom of a poly bag (like a pillow case).

Poly bag weight formula

Width x length x gauge / 1500 = lbs per 1000 bags / 2.205 = kgs per 1000 bags

Weight for 1000 12 x 18" 100 gauge polythene bags is 12 x 18 x 100g / 1500 = 14.4lbs / 2.205 = 6.53kgs per 1000 bags

Weight for 1000 24 x 32 x 60" 100 gauge gusset bags is 32 (full opening) x 60 x 100g / 1500 = 128lbs / 2.205 = 58.04kgs per 1000 bags

Weight for 1000 12 x 18 + 2" 150 gauge self seal polypropylene bags (for flap divide by 2 and add into length) is 12 x 19 x 150g / 1500 = 22.8lbs / 2.205 = 10.34kgs per 1000 bags

Poly bag size explanation

The size specification of a polythene bag can be confusing. They are typically defined by size and gauge.

If two dimensions are specified. For example 20 x 30. This means the bag is 20 inches wide and 30 inches long. These sizes refer to bag being laid flat.

If three sizes are specified. This means the bag has a gusset.

Some bags have a gusset at the sides to help the bag open out more and enable a greater volume of items to be put in. A good example is a refuse sack. If a refuse sack is 16" x 25" x 39" this means it is 16" wide opening to 25" wide when the gusset is opened with a bag length of 39".

Some bags have a gusset at the bottom to enable a wide product to fit in. A good example is a carrier bag. If a carrier bag is 15" x 18" + 3" then the bag is 15" wide by 18" long with a bottom gusset of 3".

For a explanation of gauge please refer to our gauge thickness guide.

Poly bags and the environment

Poly bags are not just reusable, they are multi-usable.

Poly bags can be recycled and recycled plastic aids the environment.

Poly bags when utilized for grocery shopping and construction can use recycled material.

Plastic and poly bags have received a bad reputation over the past few year, however plastic is easy to recycle, inexpensive to manufacture and strong for its weight and size.

Poly bag manufacturing process

Poly bags manufacturing process
Buy polytheneBuy polythene in the form of resin. The resin used in the development of poly bags are derived from natural gas or petroleum.
ExtrusionExtrusion is the process that turns the polythene resin into the film from which a polythene bag is made. It goes into a long barrel where it is pushed forward by a rotating screw. As it passes through, it is subjected to more and more heat so that it slowly melts. At the end of the barrel, the molten polythene is forced through a screen to remove any contaminants before entering the die. The die is what will give your finished item its tubular profile. The film next needs to be cooled so that it retains its shape. This will is achieved by blowing cold air on it. This should result in what is effectively a very long piece of layflat tubing. The thickness can be varied depending on the need of the packing. Lighter density bags are excellent as a packing material for items that are lightweight and need only a small shield during shipment or storage in dirty environments. Heavier weight bags can be used to pack or store more delicate materials and in abrasive environments with a lot of moisture, dust or dirt.
ConversionA converter is what turns our long tubular film into polythene plastic bags, cutting and sealing the plastic at appropriate places. Secondary operations may include printing, sealing, die cutting handles etc.

Poly bags packaging guide last updated: Jul-2023

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