Shrink wrapping may seem simple, but getting a clean, secure finish isn’t always easy.
Sometimes the film wrinkles, the seals break, or the packaging doesn’t shrink evenly around the product. These problems can slow down production, waste film and affect how the finished product looks.
The good news is that many common shrink wrapping problems can be fixed by adjusting the machine settings, checking the film or making small changes to the wrapping process.
In this guide, we’ll cover five common shrink wrapping problems, what causes them and how to fix them.
1. Dog Ears at the Corners
What you see: Small triangular flaps of excess film that stick out from the corners of the pack instead of shrinking flat. They look like folded-down page corners.
Why it happens: Dog ears form when there is too much film around the product relative to its size, or when the heat tunnel temperature is too low to fully shrink the film in the time the pack spends inside. Oversized film leaves excess material at the corners that the heat cannot pull tight. A tunnel that is too cool or a conveyor running too fast produces the same result, because the film does not reach the temperature it needs to contract fully.
The fix: Start by checking the film size. Whether you’re using a manual or automatic shrink wrapper, the goal is to use the smallest centrefold width that still provides enough film to wrap and seal the product properly.
Reducing the film width by even 20 to 30 millimetres may help eliminate dog ears. If the film size is already correct, try increasing the tunnel temperature slightly or slowing the conveyor to give the film more time to shrink.
2. Fisheyes or Pinholes in the Film
What you see: Small circular holes or thin spots scattered across the surface of the shrunk film. They look like tiny bubbles that have burst, leaving the product partially exposed.
Why it happens: Fisheyes are almost always a temperature problem. When the tunnel runs too hot, the film overheats and starts to melt through before it finishes shrinking. Polyolefin film is more forgiving than PVC in this regard, but both will develop pinholes if the temperature exceeds their working range. Uneven airflow inside the tunnel can cause localised hot spots that produce fisheyes in the same position on every pack.
The fix: Lower the tunnel temperature and check whether the issue resolves. If it only appears on certain parts of the pack, the airflow distribution inside the tunnel may need attention. Blocked or misaligned air nozzles create hot spots that overheat the film in one area while under-shrinking it in another. Cleaning the nozzles and checking their alignment is a maintenance step that gets overlooked but makes a measurable difference.
3. Weak or Split Seals
What you see: The sealed edge of the film either opens under light pressure or splits during shrinking, leaving the product partially unwrapped. In some cases, the seal looks intact but peels apart easily when pulled.
Why it happens: A weak seal points to one of three things. The sealing wire or bar temperature may be too low, leaving the film insufficiently bonded. The dwell time, which is how long the sealing bar stays in contact with the film, may be too short. Or the film layers may not be sitting cleanly against each other at the point of sealing, which happens when the product shifts during the seal cycle or when the film is not tensioned evenly.
Contamination on the sealing wire also causes inconsistent seals. Melted film residue builds up over time and creates gaps in the seal line where the heat does not transfer properly.
The fix: Check the sealing wire first. A clean, undamaged wire with the correct temperature setting resolves most seal failures. If the wire is worn or pitted, replacing it is inexpensive and immediate. For dwell time, increase it by small intervals until the seal holds under tension without burning the film. If the product moves during sealing, a guide or stop plate upstream of the sealing station can keep it positioned correctly.
4. Film Ballooning Inside the Tunnel
What you see: The film puffs up around the product as it enters the heat tunnel, sometimes inflating to the point where it lifts off the conveyor or touches the tunnel walls. The finished pack may still look acceptable after the balloon deflates, but often the film sticks to itself in unwanted places.
Why it happens: Ballooning occurs when trapped air inside the film pouch heats up and expands faster than the film can shrink around the product. A sealed pack with no vent holes traps all the air inside, and as the tunnel heats that air, it has nowhere to go. The film stretches outward instead of contracting inward.
Products with irregular shapes are more prone to this because the film sits further from the surface in some areas, creating larger air pockets.
The fix: Most shrink wrapping systems include a perforation or venting option that punches small holes in the film before it enters the tunnel. These holes let the trapped air escape as the film shrinks, preventing the balloon effect. If the machine does not have a built-in perforator, an aftermarket roller with small needles can be added before the tunnel entrance. The holes are small enough that they do not affect the finished pack’s appearance or protection.
5. Uneven Shrinkage
What you see: The film shrinks tightly on one side of the product but remains loose or wrinkled on the other. The pack looks lopsided, and the presentation suffers even though the product inside is undamaged.
Why it happens: Uneven shrinkage is an airflow issue inside the tunnel. If air circulates more strongly on one side, that side heats the film faster and shrinks it first, pulling material away from the cooler side. Conveyor position matters too. A product that enters the tunnel off-centre will receive uneven heat exposure simply because one side is closer to the air source.
Film orientation can also contribute. Shrink film has a preferred shrink direction (the machine direction versus the transverse direction), and if the film is loaded incorrectly, it contracts more in one axis than the other.
The fix: Centre the product on the conveyor before it enters the tunnel. Check the tunnel’s internal baffles and air nozzles for blockages or damage. If the problem persists across different products, the issue is likely mechanical rather than operational, and servicing the tunnel’s airflow system should be the next step.
A reliable shrink wrapper supplier like Minipack Quickshrink in New Zealand can also help diagnose persistent shrink quality issues, since the cause sometimes sits with the machine setup rather than the operator technique.
Final Thoughts
Most shrink wrapping problems come down to three things: film size, temperature and airflow.
Checking these first can help you fix common issues like wrinkles, weak seals and uneven shrinking without wasting more film or slowing down production.
If the same problem keeps happening after you’ve adjusted the settings, the machine may need servicing. Worn parts or misaligned components can affect packaging quality, and changing the settings alone won’t always solve the problem.
Regular machine maintenance and using the right film can help keep your shrink wrapping line running smoothly and reduce unnecessary downtime.
