Creep
Also called: creep deflection, long-term deflection
Creep is the gradual increase in a pallet's deflection while a load stays on it over time. Wood creeps, and plastic creeps much more, especially when warm, so racked pallets sag more after days or weeks than when first loaded.
In depth: Pallet racking and deflection: rack spans, direction and sag limits
A pallet loaded into a rack deflects immediately, then keeps slowly deflecting. The extra sag is creep. It matters most for pallets stored loaded for long periods.
How tests and software allow for it
| Method | Creep allowance |
|---|---|
| ASTM D1185 | A two-hour creep test before measuring deflection |
| ISO 8611, plastic pallets | Longer creep periods, 24 or 48 hours |
| PDS | Reports estimated deflection after 30 days at the safe load |
The ASTM and ISO durations are as summarized by the Virginia Tech Center for Packaging and Unit Load Design.
What increases creep
- Higher load as a share of capacity
- Longer load duration
- Higher temperature (a large effect in plastic)
- Higher moisture content in wood, and humidity cycling
- Plastic resins and designs that are stiffness-limited
Why it matters
A plastic pallet that passes a short rack test can sag too far after weeks in a warm warehouse. Plastic racking ratings are usually governed by stiffness and creep, not by breaking strength. For wood, PDS improved its block creep modeling in version 6.11.
On a spec sheet or RFQ
State how long pallets stay loaded in the rack (hours, days, weeks), the storage temperature range, and the deflection limit. Ask whether the rating includes creep and for how long.
Common confusions
Creep is not permanent set from overload. It develops under a load the pallet is rated to carry. Some of it recovers when the load is removed, but not always all of it.
Related
- GlossaryDeflectionDeflection is the amount a pallet bends or sags under load, measured at the point of greatest movement. Racking limits are commonly about 2% of the span, and automated systems often require 0.5 in (13 mm) or less.
- GlossaryStiffnessStiffness is a pallet's resistance to bending under load, the inverse of how much it deflects. It depends mostly on the depth of the stringers or deckboards, the material's modulus of elasticity, moisture content and temperature.
- GlossaryRacking loadRacking load is the weight a pallet can safely carry while it spans the gap between rack beams with no support underneath. It is usually the lowest of a pallet's ratings and depends on the span, the direction racked and the number of beams.
- GuidesPallet racking and deflection: rack spans, direction and sag limitsIn a rack a pallet spans between two beams with nothing underneath, so it bends. Racked across the length (stringers span about 40 to 44 in on a 48 in pallet) is usually stiffer than across the width (deckboards span about 36 in). Common deflection limits are about 2% of span, or 0.5 in or less for automated storage.
- StandardsISO 8611: flat pallet test methods, performance and working loadsISO 8611 is the international standard for testing new flat pallets. Part 1 gives the test methods, Part 2 the performance requirements used to set a nominal load, and Part 3 how to determine the maximum working load for a known payload and support condition. Parts 1 and 2 were revised in 2025; Part 3 dates from 2011.
More in Performance and engineering
- GlossaryConcentrated loadA concentrated load is a load that bears on one or a few small areas of the pallet deck instead of spreading over it, such as drums, machinery feet or a coil. It usually gives a much lower safe load than the same weight spread evenly.
- GlossaryDurabilityDurability is a pallet's ability to survive repeated handling, measured as the number of trips or handling cycles before it needs repair or is scrapped. It is driven by fastener quality, lead board width, member thickness and species density.
- GlossaryDynamic loadDynamic load is the weight a pallet can safely carry while it is being moved, supported on forklift tines, a pallet jack or a conveyor. It sits between the static rating and the racking rating.
- GlossaryLoad bridgingLoad bridging is the effect of a stiff unit load spanning across the pallet's weak points, so the packaged product carries part of the load and the pallet deflects and stresses less than it would under a flexible load of the same weight.
- GlossaryLoad capacityLoad capacity is the maximum weight a pallet can safely carry under a stated support condition. It is always quoted per condition: static (on the floor), dynamic (on forks or a pallet jack) and racking (spanning rack beams), and the racking figure is usually the lowest.
- GlossaryPallet tripA pallet trip is one complete cycle of use: the pallet is loaded, moved through the supply chain, unloaded, and made available for its next load. Durability and cost per use are both measured in trips.
Last reviewed 2026-09-24. 263 words.