Toilet Paper Thickness Measurement: Step-by-Step Testing Procedure and Standards

Toilet paper thickness is one of the most important physical quality indicators for tissue products, directly influencing softness, absorbency, roll length, and consumer perception. Accurate thickness determination requires standardized sampling, conditioning, and instrument operation in accordance with ISO 12625-3 and related national standards. This article explains the complete testing procedure, from laboratory conditioning to final reporting, for manufacturers, quality engineers, and accredited third-party laboratories.

Technical Overview

Thickness, also referred to as caliper, is a fundamental structural property of toilet paper that reflects the bulk, loft, and cushioning character of the sheet. Because toilet paper is a creped, highly compressible, and typically multi-ply product, its thickness cannot be reliably measured with general-purpose paper instruments that apply high contact pressures. Instead, the international standard ISO 12625-3, together with the corresponding Chinese national standard series GB/T 24328, specifies a dedicated dead-weight method using a low static pressure that preserves the bulky structure of the tissue.

Within this methodological framework, three related quantities are defined: the single-sheet thickness, measured on an individual test piece under a specified contact pressure; the bulking thickness, determined on a pad of stacked plies and expressed per sheet to capture the natural loft of the product; and the apparent bulk density, calculated from the grammage and the bulking thickness. Sampling is performed according to ISO 186, and all test pieces are conditioned in the standard atmosphere defined by ISO 187 before measurement.

Testing Samples

Finished Toilet Paper Rolls

Complete rolls of bathroom tissue are randomly selected from a production batch or from finished goods inventory following the sampling principles of ISO 186. The outer wrap is removed, and the first several sheets are discarded because they may carry transfer marks or deformation from the converting process. Test pieces are then taken from different positions along the roll to represent the entire web.

Multi-Ply and Embossed Products

For embossed, laminated, or multi-ply converted products, the embossing pattern introduces local thickness variations. Specimens should normally be measured in the as-delivered ply combination, and the measurement grid should include both embossed and unembossed regions so that the reported mean value is representative of the product as a whole.

Parent Reel Samples

For process control purposes, specimens may be cut directly from the parent tissue reel. Samples are taken across the full reel width, and the sampling position is recorded so that thickness profiles and cross-direction variations can be traced back to the paper machine or the creping operation.

Testing Items

The thickness determination procedure typically covers the following test items:

• Single-sheet thickness, the thickness of one test piece measured under the standard contact pressure of 2.0 kPa.
• Bulking thickness, the per-sheet thickness of a stacked pad of ten plies, reflecting the natural loft of the product.
• Apparent bulk density, calculated as the grammage divided by the bulking thickness, expressed in kilograms per cubic metre or grams per cubic centimetre.
• Thickness uniformity, evaluated from the spread of individual readings across the sampled test pieces.

Testing Methods

Apparatus and Environmental Conditions

The measurement is performed with a dead-weight, or gravimetric, thickness tester consisting of a flat anvil and a circular pressure foot that applies a static pressure of 2.0 kPa, with a contact area and foot geometry conforming to ISO 12625-3. The displacement readout, whether digital or dial type, should have a resolution of 1 micrometre, and the parallelism between the foot and the anvil must be verified during calibration. Before testing, all specimens are conditioned in the standard atmosphere of 23 degrees Celsius plus or minus 1 degree and 50 percent plus or minus 2 percent relative humidity as specified in ISO 187, normally for at least 24 hours or until equilibrium is reached.

Sample Preparation

• Select sample units at random from the lot in accordance with ISO 186 and the relevant product standard.
• Remove packaging materials and discard the first few sheets of each roll to avoid damaged or contaminated material.
• Cut at least ten test pieces of suitable size, for example 100 mm by 100 mm, free from wrinkles, folds, tears, and visible defects.
• Handle specimens by the edges only, avoiding any finger pressure, folding, or compression that would permanently reduce the bulk.
• Condition all test pieces in the controlled laboratory atmosphere before measurement.

Step-by-Step Measurement Procedure

• Verify the zero point of the instrument with the foot resting on the empty anvil, and confirm calibration using certified gauge blocks.
• Raise the pressure foot and place a conditioned test piece flat on the anvil, centred under the contact area.
• Lower the pressure foot gently and without impact so that the full 2.0 kPa static load is applied gradually to the specimen.
• Allow the reading to stabilize, which typically occurs within a few seconds of loading, and record the thickness value to the nearest micrometre.
• Lift the foot, remove the specimen, and repeat the measurement on the remaining single-sheet test pieces.
• For bulking thickness, stack ten plies one on top of another without compressing them, measure the total thickness of the pad, and divide the result by ten to obtain the per-sheet bulking thickness.
• Determine the grammage of matching specimens in parallel, using the method of ISO 12625-6, so that apparent bulk density can be calculated.

Calculation and Reporting

The arithmetic mean of all valid single-sheet readings is calculated as the thickness result, and the mean of the pad measurements is reported as the bulking thickness. Apparent bulk density is obtained by dividing the grammage by the bulking thickness, with consistent units. The test report should include the mean, maximum, and minimum values, the standard deviation or coefficient of variation, the number of test pieces, the instrument pressure and contact area, the conditioning atmosphere, and full identification of the sample and the standards applied.

Applications

Thickness data serve multiple purposes across the tissue industry. Production departments use it for routine quality control of creping, embossing, and rewinding operations, since process drifts appear quickly as thickness changes. Product development teams rely on thickness and bulk density when optimizing ply counts, basis weight reduction programmes, and embossing designs that balance hand feel with material economy. Compliance verification against product specifications, such as GB/T 20808 for tissue products, depends on standardized thickness measurement, and accredited third-party laboratories apply the same procedure for certification, supplier qualification, and the resolution of trade disputes. Distributors and packaging engineers also use nominal roll dimensions and thickness data to optimize carton fill and transport efficiency.

FAQ

Why is a low contact pressure used for toilet paper?

Toilet paper is a creped, low-density material whose value lies in its bulk and loft. High contact pressures, such as those used for printing papers, would crush the crepe structure and give unrealistically low and inconsistent readings. The 2.0 kPa pressure defined in ISO 12625-3 preserves the structure while still ensuring reproducible contact.

What is the difference between thickness and bulking thickness?

Thickness is measured on a single sheet and reflects the compressed caliper of one ply, while bulking thickness is measured on a stack of ten plies and divided by ten, capturing the natural air-filled loft between sheets that consumers perceive as softness and volume.

How many measurements are required?

A minimum of ten test pieces is generally specified to ensure statistical reliability. More measurements may be taken for embossed or highly variable products so that both patterned and unpatterned regions are represented in the mean value.

Should embossed toilet paper be measured as delivered?

Yes. Embossed products are normally tested in their as-delivered ply combination, because the embossing contributes to the bulk and performance of the finished product. Separating plies is only done for special investigative purposes, and it should be clearly noted in the report.

Which standards govern the procedure?

The core method is defined in ISO 12625-3, with sampling and conditioning governed by ISO 186 and ISO 187 respectively, grammage determined by ISO 12625-6, and the corresponding Chinese national methodology found in the GB/T 24328 series. These standards provide the technical basis shared by manufacturers and accredited third-party laboratories worldwide.