Dunnage refers to the material used to secure and protect cargo within a shipping container, truck trailer, or rail car during transport. The proper use of these materials is foundational for safe and efficient logistics operations across global supply chains. Applying these protective elements effectively helps organizations mitigate risk and maintain product integrity from origin to destination.
Defining Dunnage and Its Core Function
Dunnage functions as a secondary support system, distinct from the primary packaging that immediately surrounds a product. Its purpose is solely to manage the unoccupied space and unstable nature of the total load within the transport vehicle. The primary mechanical functions of dunnage are stabilization and separation of the shipped goods.
Stabilization prevents the entire load from shifting or collapsing during sudden movements, such as braking or sharp turns common in rail freight or ocean container shipping. Separation involves creating a buffer between individual items or layers of cargo, ensuring they do not collide or rub against each other. Repetitive friction during transit can cause significant damage to the items.
The material absorbs kinetic energy and distributes pressure across the load surface. When goods are loaded onto a vehicle, dunnage is strategically placed to fill open spaces, known as “voids,” or to reinforce stacks of packaged items. This ensures the cargo acts as a single, cohesive unit, preventing internal movement.
Why Dunnage is Essential for Shipping and Logistics
The application of dunnage offers measurable benefits in supply chain management, primarily damage prevention. By restricting movement, dunnage dramatically reduces the chance of product breakage, deformation, or surface abrasion during transit. Preventing damage translates directly into cost savings by reducing replacement shipments, minimizing claims processing, and avoiding customer dissatisfaction.
Dunnage contributes to more efficient load unitization by allowing packages of varying sizes and shapes to be consolidated safely onto a single pallet or within a container. Proper void filling optimizes the use of available container space, allowing logistics managers to maximize the volume of product shipped per trip and lower the per-unit shipping cost.
A properly secured load also improves worker safety during the loading and unloading process at distribution centers and warehouses. Stabilized cargo is less likely to shift unexpectedly when doors are opened, preventing potential injury to personnel handling the freight. A well-secured load remains stable even when only partially unloaded, maintaining a predictable environment for dock workers.
Common Types of Dunnage Materials
Wood Blocking and Bracing
Wood is utilized for its structural rigidity and capacity to manage exceptionally heavy or unusually shaped cargo, such as industrial machinery or large steel components. This material is often custom cut to create blocking structures that physically lock the load against the walls or floor of a shipping vessel or flatbed truck. Wood bracing is secured using straps or nails to the container floor, creating a robust, non-yielding barrier that withstands high forces.
Inflatable Dunnage Bags
Inflatable dunnage bags, frequently made of layered paper or woven polypropylene, are designed for quickly filling voids within enclosed transport spaces like trailers or rail cars. Once placed between cargo stacks, the bags are inflated with compressed air, applying outward pressure to stabilize the surrounding load. This lightweight application is effective for bracing cargo and absorbing shock, and the bags can often be deflated and reused, offering a sustainable option for repeat routes.
Plastic and Foam Inserts
Plastic and engineered foam inserts represent a class of highly customized, reusable dunnage often employed in closed-loop supply chains, such as automotive or electronics manufacturing. These materials are precisely molded to the contours of high-value or sensitive components, ensuring a perfect fit that eliminates all movement. The custom-fit design provides superior shock absorption, making them suitable for protecting delicate parts frequently shipped between manufacturing facilities.
Corrugated Cardboard and Paper Void Fill
Corrugated cardboard is a common, cost-effective material used to separate layers of product on a pallet or to fill smaller voids within individual shipping boxes. Its layered structure provides lightweight cushioning and structural support for lighter items. Paper void fill, often shredded or crumpled craft paper, is used to quickly pack the remaining open spaces within a carton, preventing individual items from shifting inside their primary packaging. These paper-based solutions offer an easily recyclable option for high-volume, lightweight shipments.
Regulatory and Safety Considerations
International shipping mandates strict compliance regarding certain dunnage materials to prevent the spread of invasive species across borders. The primary regulation is International Standards for Phytosanitary Measures No. 15 (ISPM 15), which specifically governs wood packaging material (WPM). Any wood used for dunnage in international transit must be treated, either by heat treatment or fumigation, and marked with a certified stamp.
Failure to comply with ISPM 15 can result in the quarantine, rejection, or destruction of the entire shipment at the destination port, leading to severe delays and steep costs. Proper documentation of this treatment is necessary for smooth customs clearance.
Beyond wood, safety regulations also address the disposal and flammability characteristics of other dunnage types. Shippers must consider the environmental impact of materials like foam and plastic, opting for recyclable or biodegradable alternatives where possible. Certain materials may also need to meet fire safety standards, especially when transporting hazardous or sensitive goods.
Key Differences Between Dunnage and Primary Packaging
The fundamental distinction lies in the intended protection scope: dunnage secures the load within the transport unit, while primary packaging protects the individual product. Primary packaging is the box, wrapper, or container that directly holds the item and remains with the product until the end-user opens it. Dunnage, by contrast, is often removed from the transport vehicle upon arrival at the distribution center and discarded or recycled.
Crating materials, which are rigid structures surrounding a product, can sometimes function like dunnage by providing structural support, but their primary role is still to protect the item itself. Dunnage focuses on the dynamic environment of the shipment, managing forces like acceleration, deceleration, and vibration across the entire cargo volume.