Dunnage, Blocking, and Bracing

Quick Answer

Dunnage, blocking, and bracing help control cargo position, distribute pressure, create forklift access, and reduce movement that tiedowns alone may not handle well.

What dunnage does

Dunnage is material placed between the cargo and the trailer deck, between layers of cargo, or between cargo and tiedown devices. Its functions include: protecting the trailer deck and cargo surfaces from abrasion and pressure damage, raising cargo to allow forklift access, creating a level base for irregularly shaped cargo, and improving the friction surface under indirect tiedowns.

Common dunnage materials include hardwood boards and blocking, rubber friction mats, engineered plastic lumber, foam padding, and airbags for filling voids between cargo units. The right material depends on cargo weight, surface sensitivity, trailer deck condition, and how the dunnage will interact with tiedowns and cargo movement.

Dunnage placement affects tiedown geometry. Raising cargo on high dunnage changes the angle of tiedowns run from deck anchor points, which changes how much of each tiedown's WLL is contributing horizontal restraint versus vertical force. Poorly placed or collapsing dunnage can also create roll or tipping risk for round or irregularly shaped cargo.

Blocking: resisting specific movement

Blocking is material placed to prevent cargo from sliding in a specific direction — most commonly forward (under braking) or rearward (on grades). Effective blocking must be strong enough to handle the force it is intended to resist, attached or positioned so it cannot itself move, and appropriate for the contact surface of the cargo.

For flatbed operations, wooden blocking is commonly used to stop machinery, equipment, coils, and pipe from sliding. The blocking must be braced or secured — wedges, nails through the deck when permitted, or positioning against a structural trailer member — so that it stays in place under the same force it is blocking against.

For van operations, blocking between pallets, at the nose or tail of the trailer, and behind door-area freight serves the same function. The blocking material and attachment method must match the cargo weight and movement path.

Bracing: maintaining position under dynamic loads

Bracing is material used to hold cargo in position against forces that may come from multiple directions — lateral forces in turns, vertical forces over rough roads, and diagonal forces that combine both. Common bracing includes shoring bars, airbags, wooden braces, and engineered load securement devices.

Unlike blocking, which resists a single-direction push, bracing typically operates as a rigid structural member that prevents cargo from moving out of its loaded position. Bracing that is too light for the load, positioned against a point-loading failure, or attached at an angle that introduces leverage rather than resistance may fail before the blocking-level forces are reached.

Inside vans and reefers, bracing is often combined with airbag cushioning, load bars, and pallet pattern as part of a layered containment approach. For reefer operations, bracing must not obstruct required airflow channels.

Friction mats and slip prevention

Rubber or polymer friction mats are commonly used under flatbed loads and inside vans to increase the friction force between cargo and the trailer deck. Higher friction reduces the horizontal force that tiedowns must provide to keep cargo in place.

Friction mats are not a substitute for tiedowns — they are a supplement. The applicable regulation still requires tiedowns meeting the WLL and count requirements. However, friction mats can reduce reliance on indirect tiedowns that depend entirely on friction to work, and they can improve stability for cargo shapes that are prone to sliding.

Inspect friction mats before use. A mat that is contaminated with oil, grease, or debris has significantly reduced friction. A mat that is too narrow to extend under the full base of the cargo provides limited benefit for lateral movement resistance.

Practical Notes

Treat this page as a planning reference. Verify the current regulation, carrier policy, shipper instructions, manufacturer ratings, and equipment condition before a truck moves.