Compression testing

A compression test measures a sample’s resistance to being squashed or compressed, usually in its entirety. Using a Texture Analyser, a large flat probe is lowered onto the sample to a defined distance or force. The instrument records deformation and resistance to quantify firmness, strength, elasticity, or other texture properties.

The Texture Analyser records force versus distance or time as the probe compresses the sample. Results are plotted automatically to show deformation, yield, and recovery behaviour.

Compression tests can be performed in a number of different ways depending upon the property that is required to be measured.

Measure the Force to go to a chosen Distance

This is the most typical type of compression test. A distance is chosen to push down onto the sample and the force to achieve this distance is measured. This type of test is typical for establishing whether the application of a chosen force is large enough to cause failure or irreversible deformation in a product.

Measure recovery/relaxation of a product by holding a Distance for a chosen time: Stress relaxation

This type of test is useful for recoverable materials like foams or bread where the degree of ‘spring’ is an important characteristic. The force at a chosen deformation distance is compared with changing forces over a chosen period of time to assess whether the material relaxes or attempts to recover to its original uncompressed height which in respect of bakery products will provide an indication of staleness/freshness.

Measure recovery of a product by holding a Force for a chosen time: Creep Recovery

Creep-recovery is a test used to see how a material deforms under a constant load and how much of that deformation it can recover once the load is removed.

Instantaneous recovery – The immediate elastic spring-back that happens the moment the force is removed. When the probe load is released, you see a sudden jump in deformation (distance) in the opposite direction which represents the purely elastic component. A material with high instantaneous recovery behaves like a spring – it regains much of its shape as soon as you unload it.

Retarded recovery – The slower, time-dependent recovery that continues after the instantaneous jump, while the material gradually relaxes. After the initial step, the curve keeps moving slowly toward the original position during the recovery time. The additional distance recovered over, say, 30–300 s is the retarded recovery. This represents the viscoelastic component – the material still recovers, but only over time. A material with strong retarded recovery may feel “cushioned” or “creepy”: it deforms under load but slowly reforms when the load is removed.

Measure the expansion or disintegration of a product by holding a Force for a chosen time

Certain materials expand or disintegrate under particular circumstances. For example, bread dough expands during the proofing stage. On the other hand, once immersed in liquid, bath bombs disintegrate. A chosen small force can be applied to the surface of these materials so that the speed (change of distance with time) of expansion/disintegration and any plateau point can be measured.

Measure the Distance to go to a chosen Force

This type of compression test is suitable for measuring the compactability of a sample, for example, when compressing granules to create tablets.

TPA – Texture Profile Analysis

A two-cycle compression test for food testing, explained in detail here.

Repeat compression cycling

This type of test is for continuous cyclic testing on one sample producing one continuous graph.

When performing compression tests they can be setup in a fundamental, empirical or imitative way – see Test Types for explanation.

Compression tests can quantify a wide range of mechanical and textural properties, including:

• Firmness/Hardness - maximum force during compression
• Compressibility/Compactability - ability to reduce in volume under pressure
• Elastic recovery - ability to regain shape after compression
• Stress relaxation or Creep compliance - change in force over time under load
• Fracture force/Yield point - point of rupture or permanent deformation

Single or multiple parameters such as peak force, work of compression/decompression, force decay and slope/modulus can be collected from the graph. By analysing these parameters, users can assess how products withstand pressure, recover shape, or fail under stress.

To learn more about how these properties are measured, visit our Textural Properties page.

Compression probes and attachments vary depending on sample size, rigidity, and geometry. Selecting the correct tool ensures accurate and repeatable data.

Simple compression

Bulk compression

Some compression tests are performed in bulk where the sample is compressed in three dimensions. This type of test is needed for multi-particle products which are irregular in shape and size from piece to piece – a chosen weight or number of pieces is tested ‘in bulk’. Usually, a compressive test is the most reliable way of assessing their fracture behaviour.

Materials and bespoke probes

Standard probes come in Delrin, stainless steel or aluminium. Bespoke geometries or materials can be produced to customer specification for specialised tests.

• Compression: Use when measuring bulk deformation without penetration (e.g. whole biscuits compressed between platens) or a number of test pieces to overcome between piece variability. If the sample area ≤ probe contact area, compression principles apply. When choosing to perform a compression test of a single piece the sample dimensions must be carefully controlled to avoid the production of variability by changing sample size.
• Penetration: Use when you need to rupture a sample to mimic it being punctured by a small item, or the sample is thin, non-self-supporting, has a skin/crust or you must mimic a probe/actuation. Penetration is a suitable test choice when samples cannot be prepared to the same dimensions as the use of a probe smaller than the sample provides a consistent contact area. A penetration test is also a way of reducing the force measured when a higher load cell is not available for testing, by way of its reduced probe:sample contact area. Typical examples: apple firmness, Bloom gel strength, packaging puncture, cosmetic wax firmness.

• ASTM D695 Compressive properties of rigid plastics
• ASTM D642:00 Compression testing of shipping containers (boxes)
• ASTM D7030:04 Short term creep performance of corrugated cardboard boxes
• BS ISO 12048:1994 Compression testing of complete, filled transport packages
• ISO 604 Compressive properties of plastics (similar applications)
• AACCI 74-09.01 Determination of bread firmness
• AACCI 56-36.01 Determination of cooked pulse firmness
• TAPPI T811 Edgewise compressive strength of corrugated fibreboard
• TAPPI T822 Ring crush of paperboard (rigid support method)
• TAPPI T809 Flat crush of corrugating medium

For the attachment of smaller compression probes you may need an Adapter.