What is dunnage in shipping?

Dunnage is the material that protects freight in transit. The word covers everything placed in, around, under or between goods to stop them moving and absorb the bumps of the road: crumpled kraft paper inside a carton, foam around a machined part, an inflatable bag wedged between two skids, lumber blocking a crate in place, a rubber mat stopping a pallet from creeping. If it isn’t the product and it isn’t the box, but it’s there to prevent damage, it’s dunnage.

The term is old — it originally meant the loose wood and matting laid in a ship’s hold to keep cargo off the wet hull and stop it shifting at sea. The materials have changed; the job hasn’t.

The three jobs dunnage does

Dunnage earns its place by doing one or more of three things:

• Filling voids. Empty space is where damage starts. A part loose inside a carton, or a gap between skids in a trailer, gives freight room to accelerate before it hits something. Void fill removes the runway.
• Cushioning. Roads transmit shock and vibration into the load. Foam, paper and air bags absorb it before it reaches the product — which matters most for anything machined, calibrated, finished or fragile.
• Bracing and friction. Blocking, bracing and anti-slip mats stop a load from sliding as the truck brakes, corners and pulls away. A load that can’t move can’t build momentum, and momentum is what breaks freight.

Common types of dunnage and when to use each

Type	What it is	Best use
Kraft paper / void fill	Crumpled or padded paper	Filling space inside cartons around lighter goods
Foam sheets and inserts	Cut or moulded foam	Cushioning machined, finished or fragile items
Inflatable dunnage bags	Air bags inflated in place	Filling gaps between skids or between freight and trailer walls
Wood blocking and bracing	Lumber cut and fastened to the deck	Immobilizing machinery, crates and heavy irregular pieces
Corner boards (edge protectors)	Rigid L-shaped strips	Protecting carton edges under strapping and stretch wrap
Rubber / anti-slip mats	High-friction matting	Stopping pallets and unbanded items from creeping
Moving blankets	Heavy padded blankets	Protecting surfaces where freight could contact walls or other freight

None of these are exotic — most are available from any packaging supplier, and the right choice usually costs a fraction of the freight it protects.

Using dunnage on a skid

On a pallet, dunnage works from the inside out. Fill cartons so their contents can’t rattle, and so the boxes themselves don’t crush when stretch wrap compresses the stack. Fill gaps between cartons on the same layer — a tight layer is a strong layer. Put corner boards under banding so the strap tension protects the load instead of cutting into it, and consider an anti-slip sheet between the pallet deck and the first layer if the goods are prone to creeping. A flat top sheet caps the unit against dust and light impact.

Dunnage supports a well-built pallet; it doesn’t rescue a bad one. Stacking pattern, weight distribution and wrap technique come first — our guide to pallet building best practices covers that foundation, and if you’re new to palletized freight, start with what a skid is in shipping.

Dunnage inside the truck

The second place dunnage works is between the freight and the vehicle. Skids in a box truck get positioned tight to each other and to the walls where possible, with inflatable bags or blocking filling any gap large enough for a pallet to shift into. Straps to the truck’s anchor points handle the primary securement; blankets protect finished surfaces where contact is possible; lumber braces anything with wheels, curved bases or a footprint that straps alone can’t hold.

Responsibility splits naturally here. The shipper owns everything on and inside the pallet, because it has to be in place before the wrap goes on. The carrier owns securement in the vehicle — though what each carrier brings varies, so flag freight with unusual needs when you book. The payoff for getting both halves right is simple: freight that arrives the way it left. Our guide to preventing freight damage on skids goes deeper on where damage actually happens and how to stop it.

When dunnage matters most

Some freight barely needs it — a solid cube of uniform cartons, wrapped tight on a good pallet, largely protects itself. Dunnage becomes critical when the load is irregular: mixed carton sizes that leave voids, machinery with protrusions, fabricated metal with finished edges, partial pallet layers, or a single heavy item that can’t be boxed. It also matters more on longer runs, where hours of road vibration will find any looseness a short hop across town would forgive.

A quick habit worth building: when freight arrives damaged, look at what the dunnage was doing. Crushed corners point to missing edge protection; scuffed faces to missing blankets or wrap; internal damage in an intact carton to missing void fill. The failure almost always names its own fix.

Palletized freight is the core of what we do — skids and pallets are roughly 60% of what Sonic Transport moves across the GTA, Golden Horseshoe and Southern Ontario, and our skid and pallet service sees every kind of load and every kind of packing, good and bad. If you’ve got palletized freight to move and want it to arrive the way it left, tell us what’s shipping and a real person will set up the run.