Sanitary Napkin Moisture Discharge Performance Testing: Standards, Methods and Applications

Sanitary napkin moisture discharge testing evaluates how effectively a sanitary pad absorbs liquid, resists rewet under pressure, and transmits water vapor to keep the skin surface dry and comfortable. This article provides a comprehensive technical overview of the key test items, applicable standards such as GB/T 8939, ASTM E96 and ISO 2528, sample requirements, and laboratory methods commonly used by accredited third-party laboratories.

Technical Overview

Moisture discharge performance is one of the most critical functional attributes of a sanitary napkin. It describes the ability of the product to rapidly draw liquid away from the skin, lock it inside the absorbent core, prevent fluid from returning to the surface under body pressure, and allow water vapor to escape through the backsheet. Poor moisture management leads to a persistent damp sensation, skin maceration, irritation, and an elevated risk of microbial growth.

A modern sanitary napkin is a multilayer composite consisting of a permeable topsheet (typically a hydrophilic nonwoven), an acquisition and distribution layer, an absorbent core combining fluff pulp with superabsorbent polymer (SAP), and a fluid-impervious but often vapor-permeable backsheet film. Moisture discharge testing therefore addresses the entire liquid transport chain: penetration through the topsheet, distribution and retention in the core, dryness of the surface under load, and vapor breathability of the backsheet.

Manufacturers, brand owners, and regulatory bodies rely on standardized laboratory test methods to quantify these properties. In the Chinese market, products are typically assessed against GB/T 8939 for absorption-related performance and GB 15979 for hygiene requirements, while international buyers frequently reference ISO, ASTM, and EN methods for vapor permeability and absorbency evaluation.

Testing Samples

Finished Products

Complete sanitary napkins and panty liners of all categories can be tested, including regular day-use pads, extended night-use pads, winged pads, ultra-thin pads, and reusable cloth pads. Finished product testing reflects real-world performance of the full composite structure and is the basis for most compliance and claims verification programs.

Component Materials

Individual materials may be tested separately to support material selection and supplier qualification. Common component samples include topsheet nonwovens, acquisition and distribution layers, absorbent core substrates, and breathable polyethylene backsheet films. Component-level testing is especially important for water vapor transmission rate (WVTR) evaluation, since the backsheet film is the primary barrier governing breathability.

Sample Preparation and Conditioning

All samples should be conditioned prior to testing in a standard atmosphere, typically 23 ± 2 °C and 50 ± 5 % relative humidity, for a period of at least 24 hours unless otherwise specified by the relevant method. Samples must be free from creases, contamination, and prior liquid exposure, and should be handled with gloves to prevent contamination of hydrophilic surfaces. Test fluid, typically a 0.9 % sodium chloride saline solution or a formulated synthetic test fluid, must be prepared at the concentration and temperature specified by the method.

Testing Items

Moisture discharge evaluation typically comprises the following test items, which together characterize the full liquid and vapor management behavior of the product:

• Water vapor transmission rate (WVTR/MVTR) of the backsheet or finished product
• Air permeability of breathable layers and finished products
• Liquid strike-through time (surface penetration speed)
• Rewet amount under load (surface dryness performance)
• Free swell absorption capacity and absorption ratio
• Fluid acquisition speed under repeated gushes
• Lateral wicking and spreading distance
• Leakage resistance under pressure

Testing Methods

Water Vapor Transmission Rate Testing

WVTR is determined gravimetrically using the cup (dish) method in accordance with standards such as GB/T 1037, ASTM E96/E96M, and ISO 2528. A specimen is sealed over a cup containing either desiccant (dry cup method) or water (wet cup method), and the assembly is placed in a controlled temperature and humidity environment. The cup is weighed periodically, and the rate of mass change is used to calculate the water vapor transmission rate, expressed in grams per square meter per 24 hours. Higher WVTR values indicate a more breathable backsheet and better long-term skin dryness.

Liquid Strike-Through Testing

Strike-through time measures how quickly liquid penetrates the topsheet. A defined volume of saline or synthetic test fluid is dispensed onto the specimen surface, and the time until the fluid reaches an underlying detection layer is recorded, commonly using an electrical conductivity detection principle. Shorter strike-through times indicate faster acquisition and a drier feel against the skin. Multiple successive doses may be applied to evaluate performance over repeated gushes.

Rewet and Dryness Testing

Rewet testing, also known as back-wetting or surface dryness testing, evaluates how much absorbed fluid returns to the surface under compression. The specimen is loaded with a defined volume of test fluid, allowed to equilibrate, and then subjected to a standardized pressure through a dry absorbent filter paper or blotter sheet of known mass. The mass gain of the paper represents the rewet value. Lower rewet values indicate that the core effectively locks fluid away, reducing skin wetness and irritation risk.

Absorption Capacity and Speed Testing

Total absorption performance is assessed by gravimetric methods in which the specimen is exposed to test fluid for a defined period, drained under standardized conditions, and weighed to determine the absorption ratio or free swell capacity. Whole-product methodologies such as ISO 11948-1 and the absorption requirements of GB/T 8939 are widely applied. Absorption speed may be determined by timing fluid uptake or by recording the mass absorbed at fixed intervals.

Air Permeability Testing

Air permeability of nonwoven layers and finished products is measured with a air flow permeability tester, which determines the volume of air passing through a defined specimen area at a fixed pressure differential. This test supports the breathability claims frequently made for breathable-film backsheets and porous nonwoven components.

Applications

Moisture discharge testing results serve multiple functions across the product lifecycle:

• Research and development optimization of topsheet, core, and backsheet material combinations
• Quality control and batch release testing during mass production
• Regulatory compliance verification for market entry, including conformity with GB/T 8939 and GB 15979 requirements in China
• Substantiation of marketing claims such as breathable, instant absorption, and dry surface
• Supplier qualification and comparative benchmarking of competitive products
• Export documentation and buyer acceptance for international trade
• Failure analysis of leakage, dampness, and skin irritation complaints

Accredited third-party laboratories provide independent test reports that are widely accepted by retailers, regulatory authorities, and overseas buyers as objective evidence of product performance.

FAQ

What is moisture discharge performance in sanitary napkins?

Moisture discharge performance refers to the combined ability of a sanitary napkin to absorb liquid quickly, retain it under pressure without rewetting the skin surface, and transmit water vapor through the backsheet, thereby maintaining a dry and comfortable wearing experience.

Which standards are most commonly used for this testing?

Vapor permeability is commonly tested to GB/T 1037, ASTM E96/E96M, or ISO 2528; whole-product absorption performance is evaluated to GB/T 8939 and ISO 11948-1; and hygiene compliance is governed by GB 15979. The applicable standard set depends on the target market and the buyer specification.

How many samples are required for testing?

Typical programs require 10 to 20 finished products per test item to ensure statistical validity, although exact quantities depend on the selected method and the number of test items requested. Component testing generally requires sufficient material to cut the specified number of specimens.

How long does testing take?

Standard turnaround is usually 5 to 10 working days for routine moisture management panels, depending on the number of test items, sample quantity, and laboratory workload. Conditioning time and repeated-dose acquisition tests may extend the schedule slightly.

What is the difference between WVTR and rewet testing?

WVTR measures vapor-phase breathability of the backsheet material over time, reflecting heat and humidity dissipation, while rewet testing measures liquid-phase dryness, quantifying how much absorbed fluid is forced back to the surface under pressure. Both are necessary for a complete assessment of skin dryness performance.