Cast vs Blown Stretch Wrap: The Differences and Benefits of Each

By Michael Kralstein | Stretch Wrap

Aug 16

When it comes to making a decision on the type of stretch wrap to use, the experts at AAA Polymer are here to help guide you to the best decision. In general, there are two different types of stretch wrap: blown stretch wrap and cast stretch wrap.

There are significant differences in the two types of films ranging from the manufacturing process to the application use. Continue reading to learn more about the differences and benefits of each.

How Is Cast Stretch Wrap Made?

Cast stretch wrap is created through a cast extrusion process, which starts with a granular resin being fed into a heated screw barrel. Then, the molten resin is continuously fed through a narrow slot die. The thickness and width of the stretch wrap is actually determined by the dimension of the slot in the die.

After passing through the die, the resin is immediately fed over a chilled roller, which quickly solidifies and cools the film. Tension rollers are used to draw the wrap to the winding and slitting stations.

Advantages of the Cast Extrusion Manufacturing Process

The cast extrusion manufacturing process results in cast stretch wrap having a unique set of benefits:

  • High transparency
  • Excellent barrier for moisture, gases, and aromas
  • Uniform thickness throughout
  • No limits on the thickness of the film
  • Cast stretch wrap has a very quiet unwind

How Is Blown Stretch Wrap Made?

Blown stretch wrap is made through a blown film extrusion manufacturing process. It begins similarly with the granular resin as well as any additives being fed by a heated screw barrel. The resin is then forced into a circular die. Afterwards, the hot resin is vertically blown upward and outward, which is typically referred to as a bubble.

Instead of being cooled quickly, the bubble is cooled gradually by air as it goes up the tower. This slow cooling process is one of the reasons the wrap looks hazy and dull. Once it rises to the very top of the tower, the film is nipped together and drawn down to the winding and slitting stations with guide rollers.

Advantages of Blown Film Extrusion Manufacturing

The blown film extrusion process of manufacturing lends blown stretch wrap its own set of benefits, such as:

  • Superior puncture resistance
  • Produces less manufacturing scrap
  • Durable and provides maximum toughness
  • Blown scrap has a high level of cling

Which Stretch Wrap Can Stretch Farther?

Many tests have concluded blown stretch wrap will stretch further than cast. However, blown stretch wrap requires more force. In some instances, you may be able to achieve a greater yield or better stretch with cast stretch wrap, but the additional stretch can be counteracted by using a lower micron blown stretch wrap.

The mechanical properties of blown stretch wrap allows users to possibly down-gauge to a thinner stretch wrap while maintaining load stability on your pallets. When you use a thinner stretch wrap, you can save money and reduce the amount of plastic waste for end users.

Which Stretch Wrap Has Greater Memory?

When Linear Low Density Polyethylene (LLDPE) is stretched, the molecules within the stretch wrap excite, which causes the stretch wrap to retract. In comparing blown and cast stretch wrap, blown stretch wrap has a much higher degree of memory.

The orientation of the molecular chains produces a stretch wrap that will contract in both cross direction (CD) and machine direction (MD). Cast stretch wrap, however, has a single orientation and "softer" characteristics, which causes it to have a reduced memory.

Which Stretch Wrap Has the Best Clarity?

Cast stretch wrap is extremely clear and produces the highest levels of clarity. This clarity is directly related to how the wrap is manufactured. By casting the molten resin over a frozen roller, crystallization is reduced and clearer film is produced.

In contrast, blown film is cooled slowly, which increases crystallization and reduces the clarity. Because of this, many people choose the clarity of cast stretch wrap when using barcode scanners.

Which Stretch Wrap Has the Least Amount of Gloss?

Blown stretch wrap has less gloss. This attribute reduces the amount of reflection under warehouse lighting, which allows easier product scanning and identification. Cast stretch wrap has higher levels of gloss, which is the result of the quicker cooling process as well as the types of resin used in the manufacturing. In the most warehouse operations, high gloss may not be as significant of an advantage because it may be difficult to scan or see through the film with standard warehouse lighting.

Contact AAA Polymer

Since 1974, the experts at AAA Polymer have been helping business owners choose the best stretch wrap for their needs. Regardless of the type of materials you are looking to wrap, our experts will conduct a thorough needs analysis.

Afterwards, we will suggest the material that will save you the most money and that's best for your application.

Contact AAA Polymer today for your free money-saving stretch wrap consultation.

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About the Author

Michael Kralstein started working in sales full time for AAA Polymer in February 2000. In 2006, he became the Sales Manager of our can liner division. He currently manages all aspects related to can liners.

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