Air Resistance of TAPPI T 460 Paper (Gurley Method)

The “TAPPI T 460 Paper Air Resistance (Gurley Method)” standard, jointly developed by the Pulp, Paper and Converting Industries Technical Association (TAPPI) and the American National Standards Institute (ANSI), describes a procedure used to measure the air resistance of paper with a circular area of approximately 6,45 cm² using a pressure difference of 1,22 kPa. The recommended range for the liquid column device is 5 to 1800 seconds per 100 mL cylinder displacement. For more impermeable papers, the time requirements become so extreme that other techniques are preferred.

This method measures the volume of air passing through the test sample and any potential air leakage across the surface. Therefore, it is not suitable for papers with rough surfaces that cannot be securely compressed to prevent significant surface and edge leakage.

For a similar air resistance measurement method that tests paper at higher pressures (approximately 3 kPa) and has higher resolution in measuring smaller air volumes, the “TAPPI T 536 Air resistance of paper (high-pressure Gurley method)” standard applies. For a method of measuring air permeability at pressures up to 9,85 kPa using both smaller and larger test areas, the “TAPPI T 547 Air permeability of paper and cardboard (Sheffield method)” standard applies.

The TAPPI T 460 standard, a widely used standard testing method, provides a reliable way to measure how resistant paper is to air passage, an important indicator of its porosity or air permeability.

This test method determines the air resistance of paper by measuring the time (in seconds) it takes for a specific volume of air (typically 100 mL) to pass through a defined area of the paper sample under a constant pressure difference.

The test area is approximately 6,45 cm² circular space. The pressure difference is 1,22 kPa, and the recommended range is 5 to 1800 seconds per 100 mL of air displacement. Units are usually reported in Gurley seconds. Higher Gurley second values indicate higher air resistance (lower porosity), meaning the paper is denser or tighter. Lower values indicate higher porosity (air passes through more easily).

The Gurley method uses a Gurley densometer, an instrument that applies slight pressure to force air through a compressed paper sample. The device typically contains a cylinder with a liquid seal or gravity-loaded material that creates the pressure. The paper is securely compressed to prevent edge leakage. Air flows through the sample, and the time it takes for a specific volume to pass is recorded.

This method involves surface seepage, therefore proper compression is crucial. It is not suitable for very thick cardboard or materials prone to significant edge/surface seepage.

Air resistance in paper indirectly reflects various structural and functional properties of the paper:

Grade of analysis: Finer fibers form denser layers with higher resistance.
Absorbency: Affects the penetration of inks, oils, water, or adhesives.
Apparent density: Tighter fiber networks increase resistance.
Filtration efficiency: This is critical for filter papers or materials used in air/liquid filtration.
Printability and coatings: These affect whether the ink stays on the surface or is absorbed.
Production processes: High-resistance papers enable vacuum processing (e.g., sheet removal during converting operations).

In recycled paper, shorter fibers generally lead to higher porosity (lower Gurley seconds) compared to virgin fiber paper.

Testing times for papers with high impermeability can be excessively long. In this case, alternative methods are recommended.

This method may involve surface seepage, which makes it less ideal for loosely structured materials.

This test remains a fundamental element in quality control across the pulp, paper, packaging, and related industries, ensuring consistent material performance.

The TAPPI T 460 standard is a fundamental test used to measure the air resistance (or conversely, porosity/permeability) of paper using the Gurley method, and is employed in the pulp, paper, packaging, printing, and related industries. It provides a standardized, repeatable method for measuring how easily air passes through paper, serving as a critical indirect indicator of various important material properties and performance characteristics.

This standard is considered important for the following reasons:

Quality control in production: Air resistance is a rapid, non-destructive inspection test used directly on paper machines. It helps monitor consistency in production by reflecting factors such as fiber fineness, sheet formation, compression, and sizing. Variations in Gurley seconds indicate problems in the paper production process at an early stage, ensuring homogeneous product quality.
It predicts absorbency and liquid permeability: Higher air resistance (longer Gurley times) is associated with lower porosity. This means less penetration of liquids such as inks, varnishes, oils, water, or adhesives. This is vital for:
Print quality: Checks how the ink sits on the surface (sharp prints) and for any excessive absorption (blurring or smudging).
Coatings and sizing: Ensures proper adhesion and performance on coated papers.
It enables automated processing in production: Papers with sufficiently high air resistance (low porosity) can be processed efficiently in converting, packaging and printing lines (e.g. for corrugated cardboard boxes or sheet-fed processes) using vacuum collectors, suction cups or lifters. Low resistance can lead to conveying errors and consequently downtime.
Evaluates filtration and breathability performance: This test assesses efficiency for materials requiring controlled air or gas flow, such as:
Filter papers (e.g., for air/liquid filtration).
Nonwoven fabrics, porous bags, or breathable membranes (e.g., for medical or packaging applications).
They exhibit structural characteristics: Gurley values indirectly measure the following:
Apparent density and Z-directional (thickness) structure.
Differences between virgin and recycled fibers (recycled fibers generally have shorter strands, leading to higher porosity).
Correlations between general paper tightness and strength.

For many years, our organization, with its competent and experienced staff, has been understanding the needs of its customers, providing the advanced testing services they require, and assisting in the establishment, implementation, and improvement of management systems. Within this framework, we also provide testing services to businesses in accordance with the "TAPPI T 460 Paper Air Resistance (Gurley Method)" standard.