How Poly Bags Are Made

Diagram of how poly bags are made
Diagram of the extrusion process

A-Pac Manufacturing produces polyethylene bags through a blown-film extrusion process.

In the blown-film extrusion process, small plastic pellets (called resin) are melted down under controlled conditions so that they become molten and pliable. They are then pressed (extruded) through a circular die gap to form a continuous tube of plastic. While it is still in this molten state, the tube is pinched off at one end and then inflated and stretched to the size and thickness of the desired finished product. The inflated bubble of plastic is drawn vertically up a tower so that it has a chance to cool before it is flattened out and wound onto a roll.

After the plastic is on a roll, it can be cut to form tubing, single-wound sheeting, or centerfold sheeting. Most often, we transform the plastic into poly bags.

Polyethylene bags are made by heat sealing and cutting rolls of film. Rolls of tubing or sheeting are fed through a machine that draws material out to the proper length. The machine then cycles to place a seal on the material and then cut it off to make an individual bag. In some cases, with small bags, machine cycle speeds may produce up to 70,000 bags per hour. In other instances, a large bag may run as slowly as 2,000 bags per hour.

The secret to producing high quality film is having good equipment that maintains a consistent flow of material throughout the process. Our modern machines employ servo drive motors for optimal control and accuracy.