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Poly Bags: A Buying Guide

Jun. 21, 2022
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The term poly bag can refer to any bag made out of plastic, though it typically references polyethylene bags. Polyethylene (PE), also referred to as polythene, is one of the most frequently-used plastics in modern manufacturing. Although PE is used across industries, one of its primary functions is as an affordable and reliable packaging material. In this context, PE is used to create bags with varying weight-bearing capacities. PE's hydrocarbon molecular structure gives poly bags the ideal combination of flexibility, tensile strength, and puncture resistance to protect contents of all shapes and sizes. 

If you're looking for a versatile and cost-effective bag for your packaging applications, this guide will help you determine exactly what poly bag suits your requirements.

 

Contents

● Selecting the Best Poly Bag for Your Application

● Poly Bag Materials

● Poly Bag Types: Flat or Gusseted?

● Common Applications

● What Size Poly Bag Do You Need?

● Custom Printed Poly Bags at Universal Plastic

 

Selecting the Best Poly Bag for Your Application

Poly bags of different shapes and materials are not always interchangeable. One poly bag may be large and dense, designed to hold concrete fill, while another is so light that it can be torn by hand. To accommodate diverse packaging needs, Fengyi Plastics offers LDPE or LLDPE poly bags in flat and gusseted designs. It's important to consider the optimal material and bag shape in advance to get the desired results. Here, we discuss these variables to help you identify the proper fit for your application.

 

Poly Bag Materials

Poly bags vary dramatically in their physical properties and potential use cases. These distinctions arise from the different forms of PE, which vary at a molecular level in both density and configuration. 

At its most basic, PE is a strand of linked ethylene hydrocarbons, which may be highly linear, highly branched, or somewhere in between. The degree of branching determines the density of the plastic as well as its performance characteristics. If the hydrocarbon chains are mostly linear, they tend to pack tightly together, which generates strong intermolecular forces that increase the material's strength. By contrast, branches interfere with the molecules' ability to pack together, so heavily-branched polymers tend to form lower-density PEs. In these plastics, the intermolecular forces pulling the chains together are weaker because of the additional distance between the atoms.

These chemical processes give rise to several primary varieties of PE:

● Low-density polyethylene (LDPE). On the opposite end of the spectrum is LDPE, which comprises branching chains of various lengths. The loose molecular structure of LDPE creates a ductile plastic ideal for crafting film wraps and grocery bags. The primary disadvantage of LDPE is its low tensile strength, which decreases durability and makes LDPE bags prone to stretching or tearing.

● High-density polyethylene (HDPE). HDPE is the most linear ethylene polymer, sometimes having just a single ethyl branch per 100 molecule chains. As a result, HDPE is the densest and strongest version of PE, typically used to create pipes and other solid components. However, HDPE can also form stiff, moisture-resistant poly bags for delicate or heavy materials.

● Linear low-density polyethylene (LLDPE). LLDPE is only slightly denser than LDPE, but it is composed of molecules with shorter branches, allowing for a more uniform linear structure. As a result, LLDPE is more durable and offers better tensile strength than other varieties. 

 

The best material for an application depends on the product to be packed:

● HDPE. Stiff and durable HDPE is typically used to package fertilizer, cement, and bulky industrial components. It may also be used for bulk quantities of grain, animal feed, or similar products.

● LLDPE. LLDPE bags are available in light to heavy gauges and are ideal for packaging foods, consumer goods, and lightweight industrial products.

● LDPE. At the lightest gauges, LDPE bags are best for single-use produce and grocery bags. Stiffer variants can form a wider array of flat and gusseted poly bags, including FDA-compliant, food-safe varieties. 

 

Poly Bag Types: Flat or Gusseted? 

Aside from material, bag type is another important consideration. Poly bags are available in both flat and gusseted designs. 

● Flat Poly Bags. As their name suggests, flat poly bags are made from seamless tubing that allows them to lay completely flat when empty. These bags can accommodate many commercial and consumer packaging applications ranging from food items to manufacturing components.

● Gusseted Poly Bags. Gusseted bags are designed to expand, with extra panels giving these bags a rectangular shape when full. Gusseted bags are ideal for packaging bulkier items. They are also useful for packaging smaller components as gusseted bags fit more product than similarly-sized flat bags, making them more efficient to store or ship.

The team at Fengyi Plastics can help you decide which type of poly bag is best for your application.

 

Common Applications

Poly bags are used to pack, store, and ship items of all kinds. 

● Bulk Packaging. Thin, plain bags are a cost-effective option for vendors that sell bulk goods of any kind. Applications range from single-use bags for bulk grocery customers to sturdier bags that contain pounds of animal feed.

● Food Packaging. FDA-approved, food-safe poly bags keep foods fresh and prevent moisture or contamination. At the same time, they offer a simple and attractive way to display bakery items, produce, and bulk foods, especially when printed with custom branding elements.

● Hardware Packaging. Small poly bags are an excellent, see-through solution for organizing hardware of different sizes or shapes. These packages are especially useful when shipping products with assembly requirements.

 

Poly bags can also protect, contain, and display non-food items of all types, including clothing, office supplies, home goods, and more.

 

What Size Poly Bag Do You Need?

Once you’ve decided on a type of poly bag, you’ll need to measure your product to determine the necessary dimensions. If you’ve chosen a flat bag, you simply need to choose the right dimensions for length by width. Consider the size of each component and the number of components you intend to place in a bag. For volumes with very small products, consider the overall volume of product that should go in each bag, then calculate the dimensions that would accommodate that volume.  It’s important to size up to account for imprecision and to allow room between components. 

For a gusseted bag, calculate the desired volume in the same way, but treat the bag as a rectangular prism when translating the desired volume to dimensions. While you should still add a bit to your measurements to ensure the bags have adequate room, the depth and shape of gusseted bags make it easier to get a close and accurate fit.

If your calculations reveal a need for a non-standard size, Fengyi Plastics can still help. As an industry leader in poly bags, we are happy to accommodate custom orders.

 

Custom Printed Poly Bags at Fengyi Plastic

Custom printed poly bags help brands stand out with colorful prints and logos, as well as nutrition facts or other specifications. At Fengyi Plastic, we offer custom printing on clear poly bags of all shapes and sizes, making it easy for clients to both attract customer attention and comply with labeling regulations.


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