Common Shrink Wrap Problems and How To Solve Them

Updated October 2026. Originally published June 2019.

Most shrink wrap problems trace back to three variables: temperature, time, and pressure. Get those three right and the majority of appearance defects, seal failures, and re-wraps disappear. The challenge is that these variables interact, so operators often chase the wrong one. The fastest way to isolate the root cause is to run an empty shrink bag at your current settings before the production run starts. If the empty bag seals cleanly, the problem is likely film sizing or a product-specific factor. If the seal is bad, it is a mechanical issue and you work through the machine settings from there.

This guide covers the defects you see on the finished package, the equipment settings that cause them, and the film and storage issues that show up before packaging even begins.

Dog Ears

Triangular protrusions at the corners of a package mean the film did not shrink down completely. The fix is almost always more heat, less film, or slower conveyor speed.

Dog ears appear when there is too much film at the corners and not enough energy to pull it tight. Work through these in order:

• Check tunnel temperature and conveyor speed together. If the conveyor is moving too fast, the package does not spend enough time in the tunnel to reach full shrink. Slow the line or raise the tunnel temp, and assess whether the ears reduce.
• Check your film width. More film than the package needs leaves excess material at the corners that cannot shrink away. Trim film width to the minimum that still closes the bag. A shrink film width calculator can help you find the right starting point.
• Check air evacuation. If the air escape hole is blocked too soon, air is trapped inside and holds the film away from the product, preventing the corners from shrinking fully.
• Check film formulation. PVC is more brittle than polyolefin after heating and tends to tent at corners instead of conforming to them. If dog ears are chronic on a PVC line, switching to polyolefin film often resolves them.
• Check package shape. Irregular corners and sharp edges on the product create geometry that is difficult to shrink evenly. There may be no perfect solution, but reducing film width and redirecting tunnel airflow toward the corners helps.

Small dog ears are common even on retail lines. How much they matter depends on whether the package goes directly to a shelf and how tightly the brand controls appearance. For products where appearance is secondary, a manageable ear at the corner is not worth slowing the line over.

Crow's Feet

Crow's feet are wrinkles radiating from the corners of a package, and they share the same root cause as dog ears: too much film and not enough heat at the corners.

The fixes overlap with dog ears, but there are a few additional levers:

• Slow the conveyor and raise tunnel temperature. Give the film more time in the heat zone.
• Reduce air evacuation rate and redirect airflow toward the saggy spots rather than away from them.
• Look at your perforation pattern. Too many perforations, or perforations in the wrong locations, prevent the film from building up the internal pressure it needs to pull tight. Reducing the number of perforations or repositioning them toward the problem corners can make a meaningful difference.
• If you are using a shrink gun rather than a tunnel, make an additional pass directly over the wrinkled corners.

Fish Eyes

Round or oval distortion patterns on the surface of a package indicate the film shrunk unevenly, almost always because of insufficient heat or uneven airflow through the tunnel.

• Raise tunnel temperature and, counter-intuitively, increase conveyor speed slightly. The goal is uniform heat application, not maximum dwell time.
• Check air velocity and direction. If the tunnel's blowers are not moving air consistently across the package, some zones will be underheated while others are fine. Inspect the air intake screens for clogged or melted polymer blocking airflow.
• Reduce the amount of film around the package so the film has less material to pull against.
• Review your perforation setup. Too many perforations allow heat to escape too quickly, leaving cold spots that produce fish eye patterns. Check that perforation pins are sharp and set to the correct depth. Dull or too-deep pins tear the film instead of puncturing it cleanly, creating weak spots that distort under heat.

Angel Hair

Angel hair, the fine strands of melted film trailing from the seal area, means the sealer is not cutting the film cleanly. The seal bar or wire is too cool, or the timing is off.

• Check sealing wire temperature. If it is too low, the film stretches away from the wire before it is fully cut. Raise the temperature in small increments until the cut is clean.
• Inspect clamp pressure and evenness. An uneven clamp cuts cleanly in some spots and drags in others. A consistent, even clamp pressure across the full seal width eliminates this.
• Check conveyor speed relative to sealer cycle time. If the sealer opens before the cut and seal cycle is complete, the film pulls away partially melted. The sealer needs enough dwell time to finish before the package advances.
• Inspect the sealing wire and Teflon pad for buildup. Polymer residue on the wire acts as an insulator and causes uneven heat transfer. Clean the wire before each run.

Ballooning

Ballooning happens when air trapped inside the sealed bag expands under tunnel heat and inflates the film. The standard fix is pre-perforated film that vents as it shrinks.

Pre-perforated film has small holes distributed across the roll that are nearly invisible once the film is shrunk. Whether you need it depends on the product and the bag configuration. If you are currently using un-perforated film and seeing ballooning consistently, switching to pre-perforated film is the most direct solution.

Also minimize the amount of air sealed into the bag before it enters the tunnel. A tighter bag wrap with less headspace reduces the volume of air that needs to escape. If using pre-perforated film, confirm the perforations are positioned so they are not sealed into the seam where they cannot vent.

Split Seals

Split or failed seals are the highest-stakes problem on a shrink line because they mean damaged product, triggered tamper-evidence failures, and potential product loss in transit.

Address a split seal problem immediately rather than running through it. The causes:

• Seal bar temperature is off. Too cold and the film does not bond; too hot and the seal is brittle and breaks under tension. Use the calibration method: start at the lowest temperature where the film will seal, then raise in increments of 5 to 20 degrees Fahrenheit until you reach a consistent, clean seal at your chosen line speed.
• Clamp pressure is uneven. An inconsistent clamp produces seals that are strong in some spots and weak in others. Check pressure across the full bar width and adjust so contact is even.
• Film gauge is too light for the product. If the product has sharp edges, weight that stresses the seal, or a shape that concentrates tension on one spot, a heavier gauge film may be the answer. Review your film specification against the actual demand the product places on the seal.
• Film has defects or is incorrectly perforated. Inspect the roll. Perforations that run too close to the seal zone weaken the bond. A bad roll will show visible inconsistencies.
• Sealing surfaces are contaminated. Clean the sealing wire, bar, and Teflon pad. Polymer buildup acts as a barrier and prevents a clean bond.

If seals fail in the tunnel after they initially appeared good, the problem shifts: check film tension near the seal area, increase airflow through different perforations, or increase the shrink bag size so the film is not pulling against the seal during shrink.

Holes in the Package

Burn holes or tears in the top of a finished package are almost always a tunnel temperature problem or a perforation pin setup problem.

• If the tunnel is too hot or the conveyor is too slow, the film receives more energy than it can absorb and burns through. Reduce tunnel temperature and increase conveyor speed. Any visible smoking is a clear signal the tunnel is too hot.
• If the damage appears at or near perforation points, the perforation pins are likely set too deep and are tearing the film rather than puncturing it cleanly. Dull pins produce the same result: a tear under heat stress rather than a clean vent hole. Adjust pin depth and replace dull pins.
• Make sure the film does not contact the walls or ceiling of the tunnel. Film touching a hot tunnel surface will burn at that contact point.

Equipment Troubleshooting: Sealer, Tunnel, and Film Settings

When the package defect points to a mechanical cause rather than a film selection issue, work through the sealer, tunnel, and film path systematically rather than adjusting everything at once.

Sealer troubleshooting

Start by identifying your sealer's ideal operating temperature for the film and line speed you are running. Begin at the sealer's lowest functional temperature, where the film will just barely not cut, and raise the temperature in 5 to 20 degree Fahrenheit increments until you reach consistent seals. Do this at the start of each shift, not just once at installation.

• Jagged or torn seals: Seal temperature is too low. Raise in 25-degree increments until the film cuts cleanly.
• Film taking too long to seal / overheated film at the seal zone: The sealer is too hot. Reduce temperature and, if the problem persists, check for uneven Teflon pad wear that concentrates heat in one spot.
• Angel hair: Wire temperature is too low or the clamp is uneven. See the angel hair section above.
• Uneven seals: Check clamp pressure across the full bar width. A loose or uneven clamp produces seals that fail at the weakest point.

Tunnel troubleshooting

• Package over-shrinks or film burns: Tunnel temperature is too high or conveyor is too slow. Increase conveyor speed before reducing temperature; temperature changes affect the whole tunnel while speed is easier to fine-tune.
• Under-shrink (dog ears, crow's feet, fish eyes): Tunnel temperature is too low or conveyor is too fast. Adjust in the opposite direction. Check that all air intake screens are clear of melted polymer, which reduces effective airflow and creates hot and cold zones.
• Inconsistent results across packages in the same run: Usually an airflow problem. Check that all blower ports are open and directed correctly, and that no packaging debris is blocking screens.
• Film damaging the product: Reduce conveyor dwell time, lower temperature, and reduce air velocity. If those adjustments are not enough, consider a lower-energy film with a gentler shrink force.
• Film contacting tunnel walls: Adjust bag size, product centering, or conveyor position so the package travels through the center of the tunnel aperture.

Film path and static troubleshooting

Static electricity is a common and frequently overlooked cause of film tracking problems, matting, and tension irregularities on shrink lines. Most shrink film is static-prone by nature.

• To check for static: Hold a small piece of film about one inch from the machine frame or another conductive surface. If the film is attracted to the surface, the film is carrying a charge.
• Grounding fix: Confirm the equipment uses a three-prong plug and the machine frame is connected to a grounding source. If the film is still tracking or matting after grounding checks, lightly rough up the polished or shiny surfaces the film slides across with fine-grit sandpaper. Polished surfaces generate friction-induced static. A metal tinsel strip or an air ionizer mounted near the film path can also pull static off the roll continuously.
• Blocking (film layers fused on the roll): Film that has been stored in high temperatures can partially fuse between layers. Lay the roll flat on a concrete floor overnight in a temperature-controlled area. If blocking is chronic, review storage conditions. Most shrink film should be stored away from heat sources and used within one year of receipt.
• Film not opening: Static cling is the most common cause when flat film will not separate at the bag opening. Use the grounding and static elimination steps above.

Film Storage and Quality Issues That Start Before the Line

Some shrink wrap problems begin in the warehouse, not on the line. Improperly stored or aged film produces defects that no machine adjustment will fix.

• Yellowing: Shrink film that has been stored past its shelf life or has been exposed to prolonged UV light will begin to yellow. For most films, the shelf life from date of receipt is one year unless the supplier specifies otherwise. Film stored past that point may also show reduced clarity and inconsistent shrink performance.
• Cracking: Storing film in extreme cold causes the film to become brittle and crack during unwinding or sealing. Bring cold-stored film to room temperature before running it.
• Gauge variation: Shrink film is manufactured to an average gauge, and the actual thickness varies across a roll. A roll labeled 45 gauge may measure 42 gauge in some spots and 48 gauge in others. If you are measuring film for quality checks, measure multiple points across the roll and use the average, not a single reading. Consistent gauge variation is normal; large deviations point to a quality problem with the roll.
• Clarity issues not caused by age: Improper storage, such as exposure to chemicals, solvents, or contaminated airflow in the storage area, can cloud film before it is ever run. Store film in a clean, dry area away from chemicals.

If you are troubleshooting a chronic appearance problem and the machine checks out, pull a fresh roll from a different lot and run a test. If the problem disappears, the issue is with the film lot, not the equipment. For help selecting the right shrink film for your application, including gauge, formulation, and perforation options, reviewing specifications against your actual product and line requirements is the right starting point.

Industrial Packaging, founded in 1953 and based in Webster, Massachusetts, sells shrink film, packaging machinery, and machinery parts, and services packaging machinery. The service technician can run film tests and, for facilities in the Northeast, visit your plant. For applications outside the Northeast, travel is available when the customer covers travel and lodging. To discuss a specific shrink wrap problem, call (800) 233-5288 or visit the technical service page.

Frequently Asked Questions

More questions plant and purchasing teams ask on this topic.

Does switching from PVC to polyolefin film require changes to machine settings?

Yes, in most cases. Polyolefin film generally requires lower sealing temperatures than PVC and responds differently to tunnel heat and airflow. When making the switch, recalibrate your sealer temperature from the bottom up and re-establish your tunnel settings rather than carrying over the PVC parameters. Running a short test batch before a full production run will surface any adjustments needed.

How can you tell whether a shrink wrap defect is a film problem or a machine problem?

Run an empty shrink bag at your current settings and inspect the seal. If the empty bag seals cleanly and the defect only appears on wrapped products, the issue is likely related to film sizing, product geometry, or the way the product interacts with heat. If the empty bag seal is poor, the problem is mechanical and you work through sealer temperature, clamp pressure, and tunnel settings before looking at the film.

What is the right way to handle shrink film that has been sitting in storage for an extended period?

Inspect it carefully before running it. Film stored beyond its shelf life may show yellowing, reduced clarity, or inconsistent shrink behavior that no machine setting will correct. Film that has been stored in cold conditions should be brought to room temperature before use to prevent cracking during sealing and unwinding. If a roll from a suspect lot runs poorly but a fresh roll from a different lot runs cleanly, the film lot is the issue.

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