Volume reduction rate testing technology quantifies how much volume cushioning and void fill materials lose under sustained compressive loading, providing essential data for transport packaging design and quality assurance. By measuring volume retention of materials such as loose fill, air pillows, and polymer foams after static compression, manufacturers can prevent product shifting, settling, and transit damage. This article explains the test principles, relevant standards such as JIS Z 0235 and ASTM D3561, typical samples, test items, procedures, and practical applications of the technology.
Technical Overview
Volume reduction rate testing is a laboratory technique used to evaluate the ability of cushioning and void fill materials to maintain their volume when subjected to a sustained compressive load. During storage and distribution, packaged goods are frequently stacked, vibrated, and compressed, which can cause the cushioning material inside the package to deform permanently. As the fill material loses volume, free space develops inside the box, allowing products to shift, collide, and become damaged. Volume reduction rate testing reproduces these conditions in a controlled manner and expresses the result as a percentage of volume lost relative to the original volume.
The volume reduction rate is typically calculated using the following relationship: volume reduction rate (%) = (V0 − Vt) / V0 × 100, where V0 is the initial volume of the specimen before loading and Vt is the volume after the specimen has been subjected to the specified compressive stress for a defined period. A lower value indicates better volume retention and more stable cushioning performance over the distribution cycle.
Several recognized standards and test frameworks are associated with this type of evaluation, including JIS Z 0235 for volume reduction of cushioning materials, ASTM D3561 for the response of loose fill packaging materials to compression, ASTM D3574 and ASTM D3575 for flexible cellular polymeric foams, ISO 1856 for compression set of flexible cellular materials, and GB/T 8168 for static compression testing of packaging cushioning materials. Accredited third-party laboratories routinely perform these tests for packaging validation, material qualification, and quality control programs.
Testing Samples
Loose Fill Cushioning Materials
Expanded polystyrene peanuts, starch-based loose fill, biodegradable nuggets, and shredded paper are commonly tested. These free-flowing materials rely on their bulk volume to immobilize products, making them particularly sensitive to compression-induced volume loss and settling.
Inflatable Void Fill Systems
Air pillows, air column rolls, and inflatable bubble sheets can lose effective volume when film leakage, air migration, or cell collapse occurs under load. Volume reduction testing verifies whether the inflatable structure retains sufficient volume throughout the expected shipping duration.
Polymer Foam Sheets and Molded Parts
Expanded polyethylene (EPE), expanded polypropylene (EPP), expanded polystyrene (EPS), and polyurethane foams in sheet, netting, or molded form are evaluated for their resistance to long-term compression and their ability to recover after the load is removed.
Paper-Based Cushioning
Honeycomb paper wrap, crimped paper pads, corrugated inserts, and embossed kraft paper provide recyclable alternatives to plastic foams. Their volume stability under repeated compression is a key selection criterion.
Fiber and Textile Wrapping Materials
Nonwoven wraps, needle-punched felts, and natural fiber mats used for surface protection and light cushioning can also be assessed for bulk thickness loss under compressive stress.
Testing Items
Depending on the material type and the applicable standard, a volume reduction rate test program may include the following measured items:
- Volume reduction rate under a constant compressive stress maintained for a specified duration, such as 24 hours
- Volume recovery rate measured at defined intervals after removal of the load, for example after 60 seconds and after 3 minutes
- Compression set, expressed as the permanent loss of thickness or volume after unloading and recovery
- Time-dependent volume change, obtained by recording volume at multiple hold times to characterize creep behavior
- Apparent density before and after loading, determined in accordance with methods such as ISO 845, to support interpretation of the volume data
- Volume reduction after repeated or cyclic loading, which simulates multiple stacking events during multi-leg distribution
Testing Methods
The general test sequence follows internationally accepted laboratory practice, with details such as compressive stress, loading duration, and specimen geometry defined by the governing standard.
Specimen Preparation and Conditioning
Specimens are cut or filled to the dimensions specified in the test method, and their initial volume is determined geometrically or volumetrically. Immediately before testing, samples are conditioned in a standard atmosphere, typically 23 °C ± 2 °C and 50 % ± 5 % relative humidity, until mass equilibrium is reached. This minimizes the influence of temperature and moisture on the measured deformation.
Apparatus and Loading
The test uses a rigid compression apparatus consisting of parallel flat platens, a means of applying a calibrated static load, and instruments for measuring thickness or volume. For loose fill, a container of specified internal dimensions with a movable pressure plate is used so that a uniform compressive stress can be applied to the fill bed while the displaced volume is recorded.
Test Procedure
- Measure and record the initial dimensions and volume of the conditioned specimen or fill bed
- Place the specimen between the platens, or the loose fill inside the test container, ensuring uniform distribution
- Apply the specified compressive stress gradually and without shock, then maintain it constant for the required hold period
- Record thickness or volume readings at prescribed intervals during the hold period
- Remove the load and measure the recovered thickness or volume after the defined recovery time
- Calculate the volume reduction rate and, where required, the recovery rate using the recorded data
- Repeat the test on the required number of specimens and report the average and individual results
Expression of Results and Test Report
The report should identify the material and supplier grade, specimen dimensions, conditioning atmosphere, applied stress, loading and recovery durations, individual and mean volume reduction rates, and any visible structural failure such as cell rupture, film leakage, or particle fragmentation. Photographs before and after loading are recommended to document deformation modes.
Applications
- Transport packaging design: selecting void fill and cushioning materials that will keep products immobilized for the full logistics cycle, including container stacking and prolonged warehousing
- E-commerce fulfillment: qualifying loose fill, air pillows, and paper pads for automated packing lines where consistent bulk volume affects box size selection and fill quantity
- Quality control: monitoring production consistency of foam sheets, molded parts, and inflatable films against internal volume retention specifications
- Material comparison and supplier qualification: benchmarking competing cushioning materials under identical loading conditions in accredited third-party laboratories
- Sustainable packaging development: verifying that recycled-content and bio-based fills maintain adequate volume stability before substitution of conventional foams
- Failure analysis: diagnosing causes of in-transit damage when product movement inside the package is suspected
FAQ
What is the volume reduction rate?
It is the percentage of a cushioning material's original volume that is lost after the material has been held under a specified compressive stress for a defined period. It directly reflects the risk of product movement inside a package during stacking and transport.
Which standards govern this test?
JIS Z 0235 specifies test methods for the volume reduction of cushioning materials, ASTM D3561 addresses the compression response of loose fill packaging materials, and related frameworks such as ASTM D3574, ASTM D3575, ISO 1856, and GB/T 8168 cover compression set and static compression behavior of cellular and cushioning materials.
How long does a typical test take?
A single static hold commonly lasts 24 hours, followed by a short recovery measurement of up to several minutes. Including conditioning, which may require 16 to 48 hours depending on the material, a complete test typically takes two to three working days.
What load is applied during testing?
The compressive stress is defined by the applicable standard or agreed between the parties, and is chosen to represent realistic stacking pressures in the intended distribution environment. The stress is held constant with calibrated weights or a controlled loading system.
How is the result interpreted?
Lower volume reduction rates indicate better volume retention and more reliable product immobilization. Acceptance limits are set by the packaging engineer based on the allowable free space inside the package, product fragility, and the expected duration and severity of the distribution cycle.
How does volume reduction rate differ from compression set?
Volume reduction rate is measured while the load is still applied or immediately at the end of the hold period and concerns overall bulk volume, whereas compression set describes the permanent deformation remaining after the load is removed and recovery is allowed. Both parameters together characterize the creep and recovery behavior of cushioning materials.