This is Part 3 of a three-part series on summer packaging hazards in the LTL environment.
Parts 1 and 2 of this series addressed the most visible summer packaging risks: corrugated strength loss and wood mold growth. This installment covers three hazards that receive far less attention but contribute to freight damage, misrouted shipments, and load failures with surprising regularity in summer: stretch film performance, adhesive label failure, and air bag dunnage over-pressurization. None of these are dramatic failure modes, but all of them are manageable with the right specifications and operating practices.
Stretch Film and the Heat Limitation
Stretch film is an effective load stabilizer and containment tool, but sustained high temperatures, whether in warehouse storage before application or inside a trailer after application, can cause it to lose its effectiveness in ways that are not always obvious until a load arrives shifted or collapsed.
Stretch film is a thermoplastic material. As temperatures rise, the polymer chains that give the film its elastic tension begin to slide past one another more easily. The film relaxes, loses its tension, and permanently deforms rather than holding its stretch. A pallet wrapped correctly in a cool morning warehouse can become meaningfully less stable after sitting in a hot trailer for a few hours. The containment force that held the load together at origin quietly degrades over the course of the day.
High quality stretch films rely on cling properties to increase their effectiveness in holding a unit load together. In summer heat, that cling chemistry creates three distinct problems. First, film stored at high temperatures can experience cling migration, causing layers to fuse together on the roll. When fused film is applied, tear-outs during application become significantly more likely, compromising wrap integrity before the load even moves. Second, adjacent pallet loads with extreme cling migration in a trailer can lock together as their film surfaces bond under heat and pressure. When one of those loads is moved during a transfer or unloading, the locking force combined with thermally degraded film can cause significant unit load shift or damage. Third, cling chemistry oxidizes over time, losing effectiveness regardless of storage conditions, which is why shelf life management matters year-round and most critically in summer.
Managing stretch film in summer comes down to three disciplines. Store rolls in temperature-controlled environments, or at minimum in the shade at ground level in the warehouse. Enforce a shelf life policy: film type varies, but one year is generally considered the maximum. And minimize the time loads spend sitting in hot staged trailers, since every hour of heat exposure compounds the relaxation and cling degradation that began the moment the load left the wrapping station.
Labels and Adhesives: A Small Failure With Large Consequences
Shippers and carriers alike rely on adhesive labels to identify, track, and communicate handling requirements for freight, in addition to typical shipment tracking and routing labels. All labels are equally vulnerable to summer heat and humidity, and carry serious consequences when they fail. When a shipper’s identification label fails, traceability is compromised. When a carrier’s tracking label fails, the shipment can be misrouted or lost in the network entirely. Handling instruction labels, including orientation arrows, fragile warnings, and stacking restrictions, that peel away before delivery mean that subsequent handlers have no guidance on how to treat the freight.
The label face stock matters as much as the adhesive. Paper-based labels absorb ambient humidity, which causes the face stock to soften, curl, and separate from the adhesive layer. In summer conditions, a paper label applied correctly at origin can be partially detached before the freight reaches its first transfer terminal. Poly-based label face stocks resist moisture absorption and hold their bond to the adhesive layer significantly better under sustained heat and humidity, making them the more reliable choice for summer shipping environments.
The simplest solution is to specify high-temperature, moisture-resistant adhesive labels as a standard practice rather than a seasonal upgrade. The cost difference between a standard label and one rated for heat and humidity is negligible compared to the cost of a misrouted shipment or a freight claim traced back to a label that did not survive the summer.
Air Bag Dunnage and the Pressure Problem
Air bags are among the most widely used void-fill dunnage in LTL shipping, and for good reason. They are fast to deploy, reusable, and effective at preventing freight movement between loads. However, summer heat can create a problem. A trailer sitting on a hot asphalt lot or making daytime deliveries in July can reach internal temperatures well above 120 degrees Fahrenheit. Air expands as it heats, and an air bag inflated to specification at origin may be significantly over-pressurized by the time it reaches a transfer terminal, exerting damaging lateral force against freight or packaging not designed to absorb it. Over-pressurized air bags can also burst outright, leaving the void they were meant to fill completely unprotected for the remainder of the journey.
A single inflation pressure standard applied uniformly across all shipments, all lanes, and all seasons is not adequate practice. An inflation PSI that performs correctly on a January morning in Minnesota will over-pressurize in a July afternoon in Texas. Carriers and shippers who treat air bag inflation as a fixed number rather than a seasonal variable are accepting a risk that is entirely avoidable. Inflation standards should account for the anticipated thermal environment the shipment will encounter, with lower starting pressures in summer months to allow for the pressure increase that heat will inevitably produce inside the trailer.
The practical guidance is straightforward. Air bags used in summer conditions should be inflated with anticipated trailer temperatures in mind. Bags inflated at ambient dock temperature in the morning will behave differently inside a trailer that heats up over the course of an afternoon run. Shippers and carriers who rely on air bag dunnage through the summer months should factor seasonal temperature into their inflation standards before the load is tendered, not after a burst bag is discovered at the transfer terminal.
Conclusion: Managing Summer, Not Surviving It
Summer is a known condition, not an unpredictable one. The humidity that softens corrugated board, the warmth that drives mold into wood pallets, the heat that relaxes stretch film, over-pressurizes air bags, and pulls labels off freight: none of these are surprises. They arrive on the same schedule every year.
For carriers, the answer is operational discipline. Seasonal inflation standards for air bags, humidity-appropriate dunnage, heat and moisture rated labels, and open trailer doors during staged dwell time are not extraordinary measures. They are what separates a summer operation that runs cleanly from one that generates avoidable claims.
For shippers, summer is when packaging specifications are tested against real conditions rather than average ones. Damage variability peaks in summer, and specs that perform adequately in cooler months can fall short when heat and humidity remove whatever margin existed. A packaging engineer threading the needle between acceptable damage rates and lower material cost will occasionally get caught in summer. Whether that is acceptable depends on what their company has defined as tolerable, and that calculation is worth doing in April, not August.
Resources like the National Motor Freight Classification® (NMFC)® packaging testing standards and registered packaging labs exist to help shippers build requirements and specifications that hold up across seasonal conditions, not just average ones.
If your organization is evaluating packaging specifications for seasonal performance, or looking to understand where your current program may be vulnerable, contact us, and visit NMFTA’s LTL Packaging resources page.
We work with shippers and carriers across the country to build packaging programs that account for the conditions freight actually faces, including the ones that only show up in summer.
