Achieving a consistent, high-quality shrink sleeve appearance is essential in modern packaging, especially when consumer acceptance and brand integrity are on the line. Unfortunately, uneven shrinkage in shrink sleeves is a common challenge faced by manufacturers using steam tunnels or dry heat  tunnels.

The good news? Most of these issues stem from a few controllable factors.

In this blog, we’ll break down the most common causes of uneven shrink sleeve appearance, along with practical tips for diagnosing and correcting them, whether you're using steam shrink tunnels or hot air shrink tunnels.

Common Causes of Uneven Shrinkage in Shrink Sleeve Labeling

1. Misalignment on the Conveyor Chain

If your containers aren’t centered on the conveyor, they won’t receive  heat evenly, leading to distorted sleeve shrinkage, and pulling to one side.

How to fix it: Ensure bottles or containers are perfectly aligned and centered before entering the tunnel. Adjust guide rails as needed for consistent positioning.

2. Incorrect Lay-Flat Width

Using shrink sleeve film with an incorrect lay-flat width can result in poor shrink conformity. Oversized sleeves often wrinkle or shrink unevenly.

How to fix it: Double-check with your sleeve and machine  suppliers that the film dimensions match your container specifications.  Container dimensional tolerances, along with sleeve tolerances need to be taken into account when sleeve specifications are determined.  This is typically done by the machine supplier.

3. Obstructions Inside the Shrink Tunnel

Fallen bottles, loose labels, or film fragments can obstruct heat or steam flow within the tunnel, creating cold spots, and uneven internal circulation. 

How to fix it: Perform regular internal tunnel inspections before each production run. Remove debris and check for downed containers.

4. External Airflow and Tunnel Disturbances

Air movement from open doors, fans, or nearby vents can disrupt tunnel performance, causing hot air or steam turbulence.

How to fix it: Keep doors closed during operation and relocate or redirect any fans or airflow sources near the tunnel.

5.Change in Material Substrate

Change in material supplier or substrate can result in variation in sleeve characteristics and performance.

How to fix it: Always know three things about your sleeves.

1)  Where they are produced and by whom

2)  The specific type of material (including brand) of the substrate

3) The percent of shrinkage the material is capable of.  Know what works and be sure your label supplier is in compliance.

Steam Tunnel-Specific Issues Causing Uneven Shrinkage

Steam shrink tunnels provide high levels of precision and shrink quality, but they must be balanced carefully. Here are the most common steam tunnel-related causes of uneven shrink:

1. Mismatched Steam Settings

If tunnel controls aren’t set identically on both the operator and machine sides, steam distribution will be uneven.

How to fix it: Always verify that both sides of the tunnel have identical steam pressure and valve settings.

2. Steam Pipe Misalignment

Steam pipes should be mirrored across both sides. Angled incorrectly, they can apply steam unevenly across the sleeve.

How to fix it: Visually inspect pipe angles and adjust to ensure symmetrical alignment on all sides.

3. Clogged Steam Pipe Holes

Steam pipe holes can become blocked by debris or calcification, resulting in poor or uneven steam output.

How to fix it: Routinely inspect pipes for clogs. Even a single blocked hole can disrupt concentric steam coverage.

5. Excessive Steam Exhausted

Most steam tunnels require some residual steam in the chamber to maintain temperature.  Too strong an exhaust fan draws out excessive steam, increases condensation and wastes energy,   

How to fix it: Reduce exhaust blower speed to a minimum for functionality and results.

Hot Air Tunnel Issues That Cause Uneven Shrinkage

Hot air tunnels rely on consistent airflow and even heating. These systems require vigilant monitoring to avoid issues such as:

1. Malfunctioning Heating Elements

If one or more heating elements are blown, the tunnel will apply heat unevenly.

How to fix it: Check all heating elements regularly. Replace any that are damaged or non-functional.  Keep spare heating elements on hand.

2. Hot Spots in Heating Elements

Inconsistent heat within an element can create hot spots, over-shrinking one area while under-shrinking another.

How to fix it: Use thermal imaging or inspection tools to identify and replace elements with uneven heating.

3. Incorrect Blower Fan Rotation

Improper fan rotation can compromise airflow and heat distribution inside the tunnel.

How to fix it: Confirm the fan is rotating in the correct direction and at the proper speed for optimal airflow.

Consistency Is King in Shrink Sleeving

Whether you're running a steam tunnel or a hot air tunnel, uneven shrinkage in shrink sleeves almost always traces back to a handful of mechanical or environmental issues. Regular maintenance, calibration, and operator awareness can prevent most problems before they affect production.

By proactively checking the areas outlined in this guide, you’ll save time, reduce waste, and improve the visual quality of every labeled product.

Need Help Troubleshooting Your Shrink Sleeve System?

At PDC International, we specialize in shrink sleeve equipment and support. Our team is here to help you achieve flawless shrink every time. Contact our experts today.