How to Produce Kraft Bubble Envelopes vs. Poly Bubble Envelopes

Bubble envelopes are widely used across e-commerce, logistics, retail, and postal services as a lightweight yet protective packaging option. While all bubble mailers share the same basic purpose—protecting shipped items from impact, moisture, and abrasion—the materials and manufacturing processes can vary significantly. Among the most common types are kraft bubble envelopes and poly bubble envelopes, each with distinct characteristics, production requirements, and application scenarios.

For manufacturers planning to expand bubble mailer production or investors evaluating bubble envelopes making machine options, understanding the differences between these two envelope types is essential. This article provides a complete comparison of raw materials, manufacturing workflows, equipment requirements, and final product performance to help you determine which envelope type best suits your goals.

1. Overview of Kraft Bubble Envelopes and Poly Bubble Envelopes

What Are Kraft Bubble Envelopes?

Kraft bubble envelopes are made by laminating a layer of bubble film to kraft paper. The outer kraft layer offers strength, rigidity, and a premium paper look, while the internal bubble layer provides cushioning. They are widely used for shipping documents, small electronics, books, cosmetics, accessories, and other items that benefit from a more professional or eco-friendly presentation.

What Are Poly Bubble Envelopes?

Poly bubble envelopes use polyethylene (PE) film as the outer material rather than kraft paper. The surface is smooth, waterproof, and highly tear-resistant. They are common in e-commerce packaging for apparel, lightweight goods, daily products, and items where moisture resistance is a priority.

2. Raw Material Differences

Kraft Bubble Envelope Materials

• Outer Layer: Kraft paper (usually 70–120 gsm), available in white, yellow, or natural brown.
• Inner Layer: LDPE bubble film.
• Adhesives: Hot melt adhesive or water-based glue for lamination.
• Seal Strip: Hot melt pressure-sensitive adhesive tape for closure.
• Optional: Printed surfaces, reinforced seams, or eco-friendly kraft options.

Poly Bubble Envelope Materials

• Outer Layer: Polyethylene film (LDPE, HDPE, or co-extruded PE).
• Inner Layer: LDPE bubble film (made from primary or recycled material).
• Adhesives: Heat lamination or extrusion lamination—no liquid glue required.
• Seal Strip: PE-based self-seal adhesive tape.
• Optional: Colored film, anti-static film, metallized film, and custom printing.

Key Difference in Materials

3. Production Process of Kraft Bubble Envelopes

Producing kraft bubble envelopes requires a combination of paper converting, lamination, and bubble envelope forming. The process typically includes the following steps:

Step 1: Bubble Film Production

Bubble film is produced by melting LDPE resin and extruding it through a bubble forming roller that creates the iconic air-filled bubbles.

Step 2: Kraft-Lamination

The kraft paper is laminated to the bubble film using:

• Hot melt glue lamination, or
• Extrusion lamination, depending on machine type.

This requires stable tension control to avoid wrinkles or bubbles between layers.

Step 3: Cutting and Forming

The laminated sheet is fed into a kraft bubble envelope making machine where it is:

• Cut to the required size
• Folded into envelope shape
• Heat-sealed at the edges

Step 4: Peel-and-Seal Application

A hot melt adhesive strip and a silicone release liner are added to create a self-sealing closure.

Step 5: Output and Stacking

The finished envelopes are counted, stacked, and packaged.

Process Considerations for Kraft Production

• Maintaining strong adhesion between kraft paper and bubble film
• Avoiding delamination during high-speed production
• Ensuring neat, sharp folding lines despite the stiffness of kraft
• Managing higher dust content from paper materials
• Controlling moisture levels to prevent paper curling

4. Production Process of Poly Bubble Envelopes

Poly bubble envelopes are produced using a similar process to kraft envelopes but with fewer material-handling challenges due to the flexibility of PE film.

Step 1: Poly Film Extrusion (optional)

Some factories purchase pre-made film; others produce their own using blown film extrusion.

Step 2: Lamination to Bubble Film

Using heat lamination, the poly film bonds directly with the bubble film—no glue required. This results in a strong and seamless connection.

Step 3: Envelope Forming

The laminated film enters a poly bubble mailer making machine, which performs:

• Cutting
• Folding
• Heat sealing
• Side sealing and bottom sealing

Step 4: Seal Strip Application

As in kraft mailers, adhesive sealing tape is added to allow users to close the envelope.

Step 5: Finished Product Counting & Collection

The envelopes are delivered to a collection table or stacking system.

Process Considerations for Poly Production

• Poly film tension must be controlled to prevent stretching
• Heat sealing temperature must match PE film thickness
• Static electricity may attract dust; anti-static add-ons may be needed
• Film thickness directly influences envelope rigidity

5. Machinery Differences: Kraft vs. Poly Bubble Envelope Machines

While the end result appears similar, the machinery required for kraft and poly bubble envelope production has important differences.

Kraft Bubble Envelope Making Machines

• Equipped with stronger feeding and tension control to accommodate kraft paper stiffness
• Use glue lamination systems or extrusion laminators
• Require dust removal systems and stable paper guiding
• Sealers designed for thicker and less flexible substrates
• Generally slower due to the rigidity of kraft paper

Poly Bubble Envelope Making Machines

• Faster running speeds (due to flexibility of PE)
• Heat lamination systems only, with no need for glue
• Simpler feeding mechanisms
• More consistent sealing quality at low temperature
• Easier material handling and smoother production flow

Cost Comparison

• Kraft machines are more expensive due to their complexity.
• Poly machines are more cost-efficient and offer higher throughput.

Conclusion

Producing kraft bubble envelopes and poly bubble envelopes involves similar goals but different materials, processes, and equipment. Kraft envelopes deliver a natural, rigid, and premium feel, while poly envelopes offer better water resistance, flexibility, and cost-efficiency.

Understanding these differences helps manufacturers choose the right production direction, machinery configuration, and investment strategy based on market demand.

About HLGP Machinery

HLGP Machinery is a professional manufacturer specializing in bubble mailer making machines, bubble film extruders, kraft bubble envelope production lines, poly bubble envelope machines, and fully automated packaging equipment. With advanced engineering, stable machine performance, and turnkey solutions tailored to customer needs, HLGP Machinery supports global manufacturers in building efficient, high-yield bubble mailer production lines. If you are planning to expand or upgrade your bubble mailer manufacturing operations, HLGP Machinery provides reliable technology, long-term service, and scalable solutions for every production requirement.