Understanding How Plastic Bags Are Manufactured

How are plastic bags manufactured?

Made of flexible, thin, non-woven fabric, plastic film or textile, plastic bags or poly-bags are used to replace paper in major light duty packaging applications, in containing and transporting goods such as magazines, foods, powders, produce, ice, chemicals, etc. Most of the plastic bags manufactured are heat-sealed while others are bonded with adhesives and some are stitched. 

Replacing Paper Packaging

Plastic bags are available in all shapes, configurations, colors, and sizes. In many applications where paper is used for packaging, the introduction of plastic bags made way for the replacement. But like other materials, there are applications where the replacement is not functionally possible or practical.

Plastic Bags Made By Heat-SealingPlastic Machinery & Parts - Sideweld Bag Making - Dec 2013 400px-Heat_Sealing_Film_for_Permeability_Test

There are different methods used in plastic bag production and the method defines the type of plastic bag produced. Heat-sealing one or more edges of an extensible film is one method of bag manufacturing.

Methods Of Bag Manufacture

Almost all plastic bags are made by heat-sealing one or more edges of the extensible film together. The heat-sealing procedure basically determines and identifies the many different types of plastic bags. One of the three basic sealing methods used in plastic bag manufacturing is a sideweld seal.

Sideweld Seal

This sealing procedure involves a heated sealing knife or blade that is round-edged and severs, cuts and seals double layers of film when the knife is pressed down through the extensible film and into a rubberized or teflon coated backup roller. A combination of heat and pressure fuse the materials together.

Sideweld Seal Mechanism

A sideweld seal is the most common bag sealing method used in plastic bag production. The sideweld technique requires that the length of the finished bag is passed through the sideweld bag making machine perpendicular to the machine floor. The extensible film material fed into the bag making machine should be pre-folded – folded during the in-feed process or J-stock. 

Sideweld Bag Machine Features

A typical sideweld bag machine is controlled by a micro-computer. Similarly, stepping motors, servo motors, AC-flux vector drives also provide their individual functions for the machine. The bag machine is also equipped with a length control system, automatic counting and repositioning system, sealing knife temperature control system, a sealing and cutting knife as well as an automatic hole punching system – including a hole design which can be customized, 

Common Sideweld ApplicationsFotolia_57841803_XS

Plastic bags manufactured in the sideweld process are commonly used for HDPE (high density polyethylene) or LDPE (low density polyethylene) of PP (polypropylene) bags for packaging including t-shirts, garments, shoes, towels, foods – fruits, vegetables and other produce, detergents, bread, sandwiches and pastry products, hardware, and ice. 

Bottom Seal And Twin Seal

Rubbish bags rollsThe other two methods of bag manufacturing are bottom seal and twin seal. The bottom seal technique involves the sealing of the plastic film only at the bottom of the bag. This method is used to produce merchandise bags and industrial liners, vegetable and fruit bags, trash bags and other types of bags supplied on a roll. The other method is the twin seal method – a process using a dual-bottom seal mechanism that supplies heat to the top and bottom of the plastic film material.


Is your plastic bag manufactured by a sideweld, bottom seal or twin seal technique?