What Are The Foaming Test Standards For Flexible Polyurethane Foam?

Test items:

1.Density: Density = mass (kg) / volume (m³)

2.Hardness: Indentation Load Deflection (ILD), Compression Load Deflection (CLD)

3.Tensile strength and elongation at break

4.Tear strength

5.Resilience

6.Compression set

7.Flame retardancy

8.VOC emissions

Test conditions:

1.For slabstock foam, samples are taken from the center; for molded foam, samples are taken from the center or tested as a whole.

2.Newly produced foam must be cured for 72 hours under natural conditions before sampling. Samples should be kept in a constant temperature and humidity environment (23±2°C, 50±5% RH as per GB/T 2918).

Hardness – ILD vs. CLD:

The main difference between these two methods lies in the loading area. In ILD tests, the compression area is 323 cm², while in CLD, the entire sample is compressed. This article focuses on the ILD method.

ILD sample size: 38×38×50 mm. Compression platen diameter: 200 mm (with R=10 mm rounded edge). The support plate has 6 mm holes spaced 20 mm apart.

Compression speed: (100±20) mm/min.

A 5 N preload is applied as the zero point. The platen compresses the sample to 70% thickness, then releases at the same speed. This loading-unloading cycle is repeated three times for pre-compression. After that, the sample is compressed again to 25±1% and 65±1% thickness, each held for 30±1s to record ILD values.

The ratio of 65% ILD to 25% ILD is known as the “compression ratio,” which reflects foam comfort.

Tensile strength & elongation at break:

Tensile strength = Breaking load / Original cross-sectional area

Elongation at break = (Final gauge length - Original gauge length) / Original gauge length × 100%

Tear strength:

Determined by applying a tearing force to a sample of specified shape.

Sample size: 150×25×25 mm (GB/T 10808), thickness direction aligned with foam rise direction. A 40 mm notch is cut in the center along the thickness direction. The sample is clamped and pulled at 50~200 mm/min. The tearing force is recorded when the tear reaches 50 mm.

Tear strength = Maximum force (N) / Average thickness (cm)

Usually, three samples are tested and the square root of the arithmetic mean is used.

Resilience:

A steel ball of specified size and weight is dropped freely from a certain height onto the foam surface. The rebound height is measured, and the rebound rate is calculated.

Sample size: 100×100×50 mm, steel ball diameter: ∮164 mm, weight: 16.3 g, drop height: 460 mm.

Rebound rate = Rebound height / Drop height × 100%

Note: The sample must be level. The steel ball should be released from a static state. Each sample is tested three times, 20 seconds apart, and the highest value is recorded.

Compression set (permanent deformation):

After maintaining a fixed deformation under constant environmental conditions for a set time, the foam sample is allowed to recover. The permanent deformation is calculated by the ratio of the difference between the initial and final thicknesses to the initial thickness.

Compression set = (Initial thickness - Final thickness) / Initial thickness × 100%