ISO 534 Paper and Cardboard - Determination of Thickness, Density and Specific Volume

The ISO 534 Paper and cardboard - Determination of thickness, density and specific volume standard, published by the International Organization for Standardization (ISO), describes two methods used to measure the thickness of paper and cardboard:

• Measuring the thickness of a single sheet of paper or cardboard as a single layer.
• Measuring the volumetric thickness of a sheet of paper.

This standard also describes the calculation methods derived from thickness specifications:

• For apparent layer density and apparent volumetric density
• For apparent specific layer volume and apparent specific volume

This standard does not apply to corrugated cardboard. Furthermore, the "Measuring the volumetric thickness of a sheet of paper" method described above is not suitable for cardboard.

The two methods generally lead to different results. These methods are not applicable to toilet paper and toilet products. The ISO 12625-3 standard applies to toilet paper and toilet products.

The ISO 534 standard is primarily based on the following principles:

• Depending on the test requirements, the thickness of a single layer or volumetric thickness is measured using a precision micrometer.
• Calculating the apparent sheet density or apparent volumetric density when the weight and thickness of the paper or cardboard are known.
• Calculating the apparent specific sheet volume or apparent specific volumetric volume when the weight and thickness of the paper or cardboard are known.

For the purposes of this standard, the following terms and definitions apply:

• Single sheet thickness: The distance between one surface of a sheet of paper or cardboard and measured under applied static load using this test method.
• Volumetric thickness: The thickness of a single sheet of paper, calculated from the thickness of several sheets stacked on top of each other in a pack and measured under a static load applied using this test method.
• Apparent sheet density: Mass per unit volume, expressed in grams per cubic centimeter and calculated from the thickness of a single sheet. This term is typically used for paper or cardboard.
• Apparent bulk density: Mass per unit volume, expressed in grams per cubic centimeter, and calculated from the thickness of the stack. This term is typically used for paper.
• Apparent specific sheet volume: Volume per unit mass, expressed in cubic centimeters/grams and calculated from the thickness of a single sheet. This term is typically applicable to paper or cardboard.
• Apparent specific bulk volume: Volume per unit mass, expressed in cubic centimeters/grams and calculated from the bulk thickness. This term is typically applicable to paper.

If tests are being conducted to evaluate a batch, the sample is selected in accordance with the ISO 186 standard. If tests are being conducted on a different type of sample, it is necessary to ensure that the test pieces taken are representative of the selected sample. Before starting the test, the sample is conditioned in accordance with the ISO 187 standard.

Test pieces are prepared under the same standard atmospheric conditions used to prepare the sample. Areas containing folds, wrinkles, cracks, or other defects that could affect the results should be avoided.

The ISO 534 standard includes precise methods for measuring the thickness of paper and cardboard. Paper and cardboard are compressible materials. Accurate thickness data helps determine how the material will perform in printing, packaging, folding, or stacking applications.

The thickness (often referred to as caliper thickness) directly affects the following:

• Print quality: Ink absorption and print performance.
• Packaging performance: Stacking strength, box rigidity, and material utilization.
• Transformation processes: Cutting, folding, and gluing.
• Density and bulk: Affect perceived quality, opacity, stiffness, and weight-to-volume ratios.
• Quality control: Ensuring consistency between production batches.

Apparent density and specific volume help manufacturers and users understand how fluffy or compact the sheet is. This is especially important for tissues, cardboard, or specialty papers.

The described test method requires a high-precision dead-weight micrometer (paper test micrometer) that applies controlled static pressure to prevent uneven compression of the material. The basic requirements are as follows:

• Specific pressure applied to the measuring probe (typically around 50 kPa or as defined in the standard).
• Proper sample conditioning (temperature and humidity control, typically 23 degrees Celsius and 50 percent relative humidity).
• For statistical reliability, multiple measurements should be taken from different points on the sample.
• Clear procedures for single-leaf and multi-leaf (volume increase) testing.

This standard ensures comparability among laboratories worldwide, emphasizing that results depend largely on the equipment and pressure used.

The ISO 534 standard generally uses the following:

• Paper and cardboard manufacturers
• Packaging converters and printers
• Quality control laboratories
• Manufacturers of testing equipment (many thickness gauges are designed according to the ISO 534 standard)
• End users in sectors such as publishing, food packaging, pharmaceuticals and consumer goods.

This standard is widely adopted and harmonized, and is used as a reference in many national standards.

This latest update to the standard includes technical improvements to enhance repeatability and accuracy in measurement procedures.

The ISO 534 standard is essential because it provides a consistent and reliable method for measuring the thickness, density, and specific volume of paper and cardboard materials. Without this standard, results from different laboratories or manufacturers would vary significantly, making quality control and trade difficult. This standard is considered important for the following reasons:

• Ensures measurement consistency: Paper thickness can vary depending on pressure, equipment, and method. This standard defines precise test conditions, such as applied pressure and measurement technique, ensuring results are comparable worldwide.
• It supports quality control: Manufacturers rely on it to maintain the homogeneity of product characteristics. Consistent thickness and density are critical for print quality, packaging durability, and converting processes (cutting, folding, lamination).
• It enables fair trade and specifications: Buyers and suppliers can agree on product specifications using a common reference. This prevents disputes about whether the material meets the requirements.
• Physical properties are linked to performance: Thickness and density directly affect stiffness and durability, opacity and print quality, and volume (important in packaging and publishing).

For many years, our organization, with its competent and experienced staff, has been understanding the needs of its clients, providing the advanced testing services they require, and assisting them in the establishment, implementation, and improvement of management systems. Within this framework, we also provide testing services compliant with the ISO 534 standard.