In fact, different types of poly bags are developed just for their strength properties. The strongest type of plastic bag is made of HDPE, or high density polyethylene. Changes to the material that determine thickness and strength occur during the polymerization process. Let’s break this down a bit further.

What Determines Plastic Bag Strength?

Plastic bag strength is established by the way the ethylene reacts during the polymerization process. To make polyethylene, small molecules of the ethylene bind together to form a chain of molecules, called a polymer. From this principal chain, branches can start to form. The more branches that form, the thinner and less dense the resulting polyethylene. To make a denser, sturdier polyethylene, fewer branches have to form.

For example, if the main polymer chain is relatively straight with few branches, it is called High Density Polyethylene. HDPE is made of tightly packed molecules that not only make it more dense, but also less flexible. It can be used to make plastic bags that are stronger and more durable than lower density plastics.

If the polymer chain has many branches that form along the main strand, it might be MDPE or LDPE. Medium density polyethylene and low density polyethylene are more flexible than HDPE and also have a lesser resistance.

How Can You Tell Which Type of Plastic Bag is the Strongest?

The strength of a plastic bag is determined by its material and thickness. We already know that the material HDPE produces the strongest plastic bags, but what about thickness? Thicker bags are typically stronger than thinner bags of the same material. To determine the thickness of a plastic bag, or its gauge, you need to find its mil score. 

Mil is a measurement used to express plastic bag thickness. A mil is equal to a thousandth of an inch. To get an idea of how bag thickness is expressed in mils, refer to these common examples of types of plastic bags:

• Common grocery store bag: ½ mil
• Bread bag: 1.5 mils
• Clothing store shopping bag: 2 mils
• Packaging for screws or nails: 4 mils
• Extreme puncture resistance for industrial parts that are sharp or heavy: 6 mils

Which Type of Plastic Bag Offers the Best Quality?

Bag strength and thickness aren’t the only determining factor of a good quality plastic bag. HDPE, MDPE, and LDPE all have useful applications as plastic bags. The application will determine which bag qualities are essential, such as durability, clarity, and ease of opening. Let’s take a closer look at these qualities to help you understand the different advantages these qualities of poly bags offer. 

Poly Bag Durability

Bag durability doesn’t just refer to the tensile strength of the plastic. The durability of a poly bag could also mean its resistance to chemical corrosion, punctures, or regular wear and tear.

Poly Bag Clarity

Bag clarity is important in many applications where product visibility is key. For example, for many food grade poly bags, customers need to be able to see the enclosed item clearly to check for quality. A translucent or opaque bag would not serve this purpose. 

Poly Bag Ease of Opening

If you’re just looking for which plastic bag is the strongest, you might not want a bag that is easy to open, but in some applications, this is a good quality to have. Bags containing small parts like screws and nails need to keep the items together, and be strong enough to not spill the items, but also need to be easy to tear to access what’s inside.

Which Type of Plastic Bag is Best for You?

When shopping for which type of plastic bag is the strongest, consider the other needs your application might have. If strength is the most important quality, then an HDPE poly bag at a high mil strength will likely be the best type of plastic bag for your needs. However, if you’re looking for a strong plastic bag with other qualities, consider other types of poly bags that may work just as well. 

If you’re still unsure which type of poly bag is right for your application, contact A-Pac Manufacturing. We manufacture the highest-quality poly bags, with no minimum order and 2-3 week lead times. Give our team a call for more information.