Dunnage in Shipping: Choose Protection for Cartons and Pallets

Dunnage refers to materials and products used to protect, support, and secure cargo during storage and transportation; in shipping it prevents movement, cushions against shock, and helps distribute weight so cartons and pallets arrive intact. For cartons and palletized freight, dunnage choices (void fill, blocking, load supports, steel dunnage) change how much movement and damage you’ll see and how carriers accept the load.

How Dunnage Protects Cargo

Dunnage works by filling empty space, creating rigid support points, or transferring force away from vulnerable items. Void-fill materials (paper, foam, airbags) reduce relative motion inside cartons or between pallets. Blocking and bracing (timber or engineered plastic blocks, wedge-shaped pieces) stop lateral and longitudinal shift on a pallet or inside a trailer. Load supports (timber beams, pallet reinforcements, steel runners) carry concentrated vertical loads so cartons beneath are not crushed. Choosing the right combination depends on mode (truck, rail, ocean), cargo fragility, and carrier rules.

Void Fill, Blocking, And Load Supports — Three Examples

This section compares the three dunnage strategies using three practical shipping scenarios and notes expected movement and damage outcomes.

Example 1 — Consumer Electronics On A Pallet (LTL Truck): A pallet contains 40 small cartons with voids between cartons and carton walls. Best choice: airbags or foam block void-fill plus perimeter blocking. Airbags inflate between cartons and the pallet walls to stop lateral shift during cornering; timber blocking across the pallet edges prevents slip between layers. Expected result: minimal lateral movement, low crush risk if vertical stacking height and pallet capacity are respected.

Example 2 — Glass Sheet Bundles (Intermodal Or Rail): Glass sheets are heavy and brittle with very low tolerance for point loading. Best choice: timber or engineered timber cradles (blocking) and steel dunnage runners under the bundle to spread load to rail/carriage points. Blocking prevents lateral slide; steel runners distribute weight to the car or trailer floor and resist concentrated deformation. Expected result: near-zero movement and reduced breakage risk when combined with straps; incorrect void fill alone would be insufficient.

Example 3 — Mixed-SKU Pallet With Heavy Bottom, Light Top (Ocean Container): Mixed weights can create crush at the bottom and collapse under vibration. Best choice: rigid load supports—timber cross-beams between pallet decks, corner bracing, and foam panel void-fill where small gaps exist. If shipped ocean, pair with strapping and dunnage bags to reduce cargo surge during vessel motion. Expected result: good vertical load distribution and reduced crush damage; airbags plus blocking mitigate surge better than void fill alone.

Testing Movement And Damage

Simple, repeatable tests show how well a dunnage method performs before you tender freight. Use these steps and reference ASTM D4169 for laboratory-style protocols where needed:

• Lateral Shift Test: Place the pallet on a smooth floor and apply a lateral force (push or mechanical actuator) to the top—measure movement in inches or millimetres. Less than 1" lateral shift for a loaded pallet is a common operational target for LTL moves.
• Vibration/Transit Simulation: Subject the pallet/carton to vibration (truck/trailer profile) for 15–30 minutes or until movement stabilizes—document broken seals, abrasions, or collapsed cartons.
• Drop And Impact: Drop a packed carton from common handling heights (12–36") to simulate handling. Inspect for internal product damage and inspect cushioning effectiveness.
• Compression Test: Stack pallets to shipping height and measure vertical deflection and deformation of lower cartons under static load for 24–72 hours.

Record results and adjust dunnage—if cartons slip more than planned, increase blocking or use airbags; if cartons crush, add load-bearing supports or redistribute weight.

Steel Dunnage For Freight

Steel dunnage (runners, angle sections, frames) is used when loads exceed what timber or plastic can safely carry, or where repeated reuse and high compressive strength are required. Typical steel dunnage uses include heavy machinery, vehicles, and industrial components for rail or heavy truck movement. Steel is superior for point-load resistance, resists deformation from forklift tines, and doubles as a permanent support structure for unitized loads.

Operational notes: carriers may impose limits or inspection requirements for non-standard dunnage. Steel increases tare weight and may affect declared load distribution; always confirm with the carrier and follow securement regulations for the mode (see Verify Carrier And Platform Claims below).

Worked Example: Pallet With Mixed-Weight Cartons

Scenario: A 48x40" pallet holds 60 cartons each 12"x12"x12" at 15 lb per carton (total 900 lb). Cartons vary in weight and are stacked 6 high with small voids at the corners.

Step 1 — Identify risks: lateral shift in transit, toppling during handling, bottom-layer crushing.

Step 2 — Select dunnage: use two polyester cross-beams under the pallet (load support), inflatable airbags along the pallet perimeter (void fill) and three timber blocks at the pallet corners between carton layers (blocking).

Step 3 — Apply securement: strap the pallet with two 2" steel-buckle straps across the short face, install a top sheet to distribute strap pressure, and set corner protectors.

Step 4 — Test: push test—lateral movement <1"; stack compression—no visible bottom flange collapse after 24-hour load; vibration simulation—no carton abrasion. If any test fails, replace airbags with denser foam blocks and add a third cross-beam.

Dunnage Pre-Tender Checklist

• Weight And Centre Of Gravity: Confirm total weight and locate CG to decide where load supports and steel runners are required.
• Space And Voids: Identify all voids >1" and plan void-fill or blocking accordingly.
• Vertical Load Capacity: Verify pallet and dunnage compressive strength against expected stack height.
• Mode-Specific Needs: Add airbags for ocean/intermodal surge, and steel runners for rail or very heavy loads.
• Carrier Limits: Check carrier maximum pallet weight, strap rules, and any prohibition on certain dunnage materials.
• Test Plan: Run lateral, vibration, and compression checks before dispatch.

Verify Carrier And Platform Claims

Carriers and shipping platforms publish packaging and securement guidance but their statements change. Always verify with the carrier’s current documentation before tendering freight. For U.S. highway moves, use the Federal Motor Carrier Safety Administration cargo-securement rules as the legal baseline. For carrier packaging guidance, consult the packaging pages of major carriers (UPS, FedEx) or the receiving platform’s published requirements; if shipping to marketplaces or using FBA-like services, confirm platform prep rules for dunnage and acceptable materials. If you plan to use steel dunnage on a trailer or railcar, request carrier acceptance in writing because steel may affect weight declarations and handling procedures.

In short, the Dunnage you select determines how much a palletized shipment moves, how load pressure is distributed, and how much risk of damage you accept. Match void fill, blocking, and load supports to the cargo fragility and transport mode, test the assembly before shipping, and confirm carrier/platform rules—steel dunnage is ideal for heavy, point-loaded freight but requires carrier verification.