Difference Between Cast and Blown Stretch Wrap

In the realm of packaging and shipping, understanding the difference between cast stretch wrap and blown stretch wrap can greatly impact the efficiency, cost, and safety of operations. These two types of stretch films, while serving the same core purpose of securing loads, have distinctive properties and applications due to their unique manufacturing processes. This article aims to provide an in-depth comparison between cast and blown stretch wraps, detailing their similarities, differences, pros, cons, and the situations where one may be preferred over the other.

What is Cast Stretch Wrap and Blown Stretch Wrap?

Stretch wrap, also known as stretch film, is a highly stretchable plastic film that is primarily used to wrap around items, particularly on pallets, to keep them secure during storage and transportation. There are two main types of stretch wrap: cast stretch wrap and blown stretch wrap.

Cast Stretch Wrap: This type of stretch wrap is manufactured using a cast extrusion process. The process involves melting a thermoplastic material, most commonly linear low-density polyethylene (LLDPE), and then extruding it through a flat die onto a chilled roll, where it cools and hardens into a sheet. Once it’s solidified, it’s made into large rolls of film. Cast stretch wrap is known for its excellent clarity, allowing users to see the product being wrapped. It also unwinds quietly off the roll and offers a good level of cling, stretch, and tear resistance. Cast stretch wrap is typically less expensive than blown stretch wrap, making it a popular choice for many businesses.

Blown Stretch Wrap: This type of stretch wrap is produced using the blown extrusion process. Here, melted plastic is extruded upward into a bubble, using air much like a balloon. The plastic cools as it slowly comes back down, hardening into a plastic film. The process gives blown stretch wrap its unique characteristics. It is more resistant to puncture and holds loads better than cast wrap because it has higher levels of cling and tensile strength. However, blown stretch wrap is noisier when unwrapped and is less clear than cast wrap, making it harder to read labels or barcodes through the film. Despite being more expensive, it’s often preferred for loads that are more challenging to wrap or need to endure harsher shipping conditions.

Key Differences between Cast Stretch Wrap and Blown Stretch Wrap

1. Production Process: Cast stretch wrap is made using a cast extrusion process, whereas blown stretch wrap uses a blown extrusion process.
2. Cost: Generally, cast stretch wrap is less expensive than blown stretch wrap.
3. Clarity: Cast stretch wrap has greater clarity, making products and labels easier to see, while blown stretch wrap is less clear due to its manufacturing process.
4. Noise: Unwinding cast stretch wrap is a quieter process compared to the noise produced by unwinding blown stretch wrap.
5. Tensile Strength and Puncture Resistance: Blown stretch wrap is more resistant to puncturing and has a higher tensile strength, making it more suitable for heavy or irregular loads.
6. Cling: Blown stretch wrap has a higher level of cling, which can be beneficial for ensuring load stability, while cast stretch wrap has less cling.

Key Similarities between Cast Stretch Wrap and Blown Stretch Wrap

1. Material: Both types of stretch wrap are typically made from linear low-density polyethylene (LLDPE).
2. Purpose: Both are used for the same purpose, which is to secure items, particularly on pallets, for storage and transportation.
3. Stretchability: Both types of stretch wrap are highly stretchable, which allows them to be wrapped securely around items.
4. Recyclability: Both cast and blown stretch wrap are recyclable, making them environmentally friendly options.
5. UV Resistance: Both types can be treated to resist UV radiation, which can be beneficial for products stored outside for long periods.
6. Functionality: Both types can be used with various types of equipment, including handheld dispensers and automatic or semi-automatic machines.

Pros of Cast Stretch Wrap over Blown Stretch Wrap

1. Cost-effectiveness: Cast stretch wrap generally costs less to produce than blown stretch wrap, making it a more budget-friendly choice for businesses.
2. Clarity: Due to its manufacturing process, cast stretch wrap has better clarity. This allows for easier identification of products, reading of labels, and barcode scanning.
3. Quiet Unwinding: Cast stretch wrap unwinds off the roll quietly, which can be a benefit in environments where noise reduction is preferred.
4. Consistent Thickness: The cast extrusion process results in a product with a more consistent film thickness, which can result in less product waste and more efficient wrapping.
5. Less Force to Stretch: Cast stretch wrap typically requires less force to stretch, reducing the amount of energy needed to apply the wrap and potentially reducing worker fatigue.

Cons of Cast Stretch Wrap compared to Blown Stretch Wrap

1. Puncture Resistance: Blown stretch wrap typically has a higher resistance to puncture compared to cast stretch wrap. This can make blown stretch wrap a better option for wrapping sharp or irregularly shaped items.
2. Tensile Strength: Blown stretch wrap generally has a higher tensile strength, which can provide a more secure hold for heavier loads.
3. Higher Cling: Blown stretch wrap tends to have a higher degree of cling, which can result in a more secure wrap, especially for challenging loads.
4. Durability in Extreme Conditions: Blown stretch wrap often performs better in extreme cold or heat, as well as in higher levels of UV exposure.
5. Resistance to Tear Propagation: While cast stretch wrap might be more prone to initial puncturing, blown stretch wrap excels in resistance to tear propagation. Once torn, a blown film tends not to rip as easily as cast.

Pros of Blown Stretch Wrap over Cast Stretch Wrap

1. Higher Puncture Resistance: Blown stretch wrap typically exhibits superior puncture resistance, making it ideal for wrapping objects with sharp or protruding edges.
2. Superior Load Holding: Thanks to its higher tensile strength and better cling properties, blown stretch wrap offers better load holding capacity, particularly for heavy or irregular loads.
3. Better Tear Propagation Resistance: If a tear does occur in blown stretch wrap, it is less likely to spread or ‘zipper’ through the film, ensuring continued load stability.
4. Excellent Performance in Extreme Conditions: Blown stretch wrap often performs better in extreme temperatures and is less affected by UV radiation, making it a good choice for outdoor storage or shipping in harsh conditions.
5. Increased Stretch Potential: Blown stretch wrap can often be stretched further than cast stretch wrap before breaking, increasing its potential wrap yield and cost-effectiveness.

Cons of Blown Stretch Wrap compared to Cast Stretch Wrap

1. Higher Cost: Generally, blown stretch wrap is more expensive to produce and therefore typically costs more than cast stretch wrap.
2. Lower Clarity: Blown stretch wrap is not as clear as cast stretch wrap, potentially making it more difficult to identify products or read labels and barcodes through the film.
3. Noise: When unwinding from the roll, blown stretch wrap produces more noise than cast stretch wrap, which can be disruptive in some environments.
4. Requires More Force to Stretch: Blown stretch wrap typically requires more force to stretch than cast stretch wrap, which could potentially lead to increased worker fatigue over time.
5. Inconsistent Film Thickness: The blown extrusion process may result in slightly less consistent film thickness compared to the cast extrusion process, which can sometimes lead to product waste.

Situations when Cast Stretch Wrap is better than Blown Stretch Wrap

1. Budget Constraints: When budget is a primary consideration, cast stretch wrap can be a more cost-effective option due to its lower manufacturing costs.
2. Need for Clarity: When the visibility of products, labels, or barcodes is important, the superior clarity of cast stretch wrap can be an advantage.
3. Noise-Sensitive Environments: If the wrapping operation is taking place in a setting where noise is a concern, the quiet unwinding of cast stretch wrap would be preferable.
4. Uniform Loads: When wrapping uniform loads that do not have sharp edges or protrusions, the lower puncture resistance of cast wrap is less of a concern.
5. Lower Volume Applications: For operations that don’t require extreme load holding, puncture resistance, or the ability to withstand harsh conditions, the properties of cast wrap may be sufficient.

Situations when Blown Stretch Wrap is better than Cast Stretch Wrap

1. Heavy or Irregular Loads: The superior tensile strength and puncture resistance of blown stretch wrap makes it a better choice for heavy or irregularly shaped loads.
2. Harsh Shipping Conditions: For loads that are expected to endure harsh shipping or storage conditions, the durability of blown stretch wrap is beneficial.
3. Outdoor Storage: If products are to be stored outdoors, blown stretch wrap’s resistance to UV radiation can be an advantage.
4. High-Speed Automatic Equipment: Blown stretch wrap’s ability to stretch further before breaking can make it a better choice for high-speed automatic wrapping machines.
5. High Demand for Load Stability: When there’s a high demand for load stability, such as in shipping heavy, shifting loads, the higher degree of cling in blown stretch wrap can be advantageous.

Cast vs Blown Stretch Wrap Summary

Both cast stretch wrap and blown stretch wrap have their unique strengths and weaknesses. The choice between them should be driven by the specific requirements of your packaging operation. Understanding the difference between cast stretch wrap and blown stretch wrap is essential to making an informed choice that ensures efficient, secure, and cost-effective wrapping. By considering factors like load characteristics, environmental conditions, and budget, you can choose the stretch wrap that best suits your needs.

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