Plastic Bags

There are a variety of uses for plastic bags when it comes to retail products. They can be used to protect merchandise during transport, hold bulk items together during shipment, as individual retail packaging or for after purchase carriers. The purpose of the bag and the contents it will hold effect what type of plastic should be used. While many bags are made with just one plastic, more than one plastic can be combined together to fit individual product needs.

Bags are made in variable thicknesses and colors and can be embossed, compostable and have anti-static properties. The stronger and more rigid plastics can be used to make stand-up plastic pouches. These are usually used for food or liquids but can hold anything and will stand upright unaided. Plastic bags can also include various attachments such as adhesive glue strips, hooks, handles and zippers. Gussets can be added into the design of the bag to allow for higher volumes of products inside.

There are some variables that will effect the extent of the plastic properties. The one that can make the biggest difference is the thickness. The thicker the material, the higher the tensile strength (the pull the plastic can endure before it breaks). Most bags consist of one of the four plastics described below.

Polyethylene (PE) is the most commonly used plastic worldwide and is also the most commonly used plastic in bags. Generally, it is lightweight, flexible and has good chemical resistance. One property of PE is that it is tough, meaning it stretches before breaking. This stretching allows the energy to dissipate instead of immediately tearing. PE also has relatively good strength, so it can take a lot of force to break it. Because of its low cost, PE bags are often used for bulk packaging as well as retail packaging.

Two common forms of PE are Low Density PE (LDPE) and High Density PE (HDPE).  LDPE is very flexible, tough and relatively transparent. It has moderate strength and is good in applications which require heat sealing. In packaging, it is often used to make wrap-around product labels and wrap packaging for products with multiple items. Most bread and thicker newspaper bags are also made out of this.

HDPE is more opaque, stiff and has much better barrier properties than LDPE. It has high strength but lower stretch properties than other forms of PE. HDPE will also crinkle to touch. Many grocery bags are made out of this type of plastic. HDPE is slightly more expensive than LDPE.

Polypropylene (PP) is a strong plastic, meaning it can withstand a lot of pull force. It is semi-rigid and transparent in color, allowing consumers to view the product in high clarity. Compared to other plastics, it has a high melting point and is often used where a high chemical and moisture resistance is desired. Unlike PE, PP does not stretch very well. It is most commonly found with food bags since it is good at trapping moisture in and keeping air out.

Oriented Polypropylene (OPP) has a high transparency, strength and good twist retention. The barrier properties of this plastic are better than most, having high moisture and chemical resistance. OPP bags are commonly used in individual packaging as well as in greeting card sleeves and flower sleeves.

Polyvinyl Chloride (PVC) is initially a very rigid plastic. However with the help of plasticizers, PVC can be made flexible. It is a heavy duty plastic in that it is both strong and tough, and has high barrier properties. This plastic is transparent. PVC is often used for bedding bags due to its strength and resistances to both fire and water.