GMW 4726 Waterproofing Properties of Automotive Textiles

The “GMW 4726 Waterproofing Properties of Automotive Textiles” standard, developed by General Motors Worldwide (GMW), is a test standard used to evaluate the waterproofing properties of automotive textile materials. This standard typically uses a spray test to assess how effectively a textile surface resists water.

Waterproofing is a crucial property for automotive fabrics used in areas such as seat upholstery, door panels, headliners, luggage racks, and other textile-covered interior components. A fabric's resistance to water helps prevent the material from quickly wetting, staining, absorbing, and deteriorating.

The primary goal of the GMW 4726 standard is to provide a repeatable method for determining the surface water repellency of automotive textiles. Unlike water absorption tests, which determine how much water a material absorbs, water repellency tests evaluate the behavior of water droplets when they come into contact with the textile surface. A water-repellent fabric typically causes water to form droplets and remain on the surface or repel, rather than immediately penetrating the textile.

The method described in the GMW 4726 standard is defined by testing laboratories as a spray test. Generally, the test involves exposing a conditioned textile sample to a controlled spray of water. The appearance of the wetted sample is then visually assessed according to a standardized grading system. For example, 250 mL of distilled water is sprayed onto a stretched fabric sample, and the resulting surface condition is then visually evaluated on a 0-10 rating scale.

The basic concept can therefore be summarized as follows: textile conditioning, sample assembly, application of standardized water spray, visual assessment of wetting, and assignment of water repellency rating.

Sample preparation, equipment configuration, spraying conditions, evaluation criteria, and acceptance requirements are detailed in the GMW 4726 standard. These details depend on the publication of the standard and the vehicle/material specification.

In general, the testing process follows these steps:

• Sample preparation: Representative textile samples are prepared from the material being evaluated. The samples should be representative of the production material, including its structure and any relevant finishing processes.
• Conditioning: Samples are conditioned under the environmental conditions specified in the relevant test procedure prior to testing. Conditioning is important because textile moisture content and environmental history can affect wetting behavior.
• Assembly: The textile sample is placed in the testing device in the specified orientation and conditions. Published specifications indicate that the textile can be tested under controlled tension.
• Water spraying: A specified amount of water is applied to the textile using a controlled spray pattern. The aim is to create a repeatable water effect on the textile surface.
• Visual assessment: After the spraying process, the surface is examined for the following characteristics:
  • Surface wetting
  • Water spreading
  • Droplet formation
  • Water penetration into textiles
  • General view of the wetted area.

The observed result is converted into the corresponding water repellency rating.

• Evaluation: The measured or observed value is compared to the specified requirement for the relevant textile, component, or tool program. It is important to distinguish between the test method and the acceptance criterion: while this provides for the standard test procedure, the required performance level may be specified separately in the relevant material or component specification.

The GMW 4726 standard uses a visual evaluation scale of 0–10 to determine the post-spray surface appearance assessment. The basic interpretation is that the assessment represents the textile's apparent resistance to wetting. A fabric treated with a strong water-repellent should show significantly less wetting than a fabric that readily absorbs and releases water.

Typical equipment used when performing GMW 4726 testing includes:

• Waterproof/spray test device
• Spray nozzle and water distribution system
• Sample mounting or tensioning device
• Measuring cup for the specified amount of water.
• Distilled or ionized water as indicated.
• Controlled conditioning environment
• Rating system for visual evaluation.

The GMW 4726 standard is closely related in principle to the spray test approach used for textile water repellency, and laboratories often list both GMW 4726 and ISO 4920 standards together under water repellency testing.

Waterproofing can be an important performance characteristic for automotive textiles because interior fabrics may come into contact with water during vehicle use, cleaning, transportation, and exposure to environmental factors. This standard is considered important for the following reasons:

• It helps control water penetration: A waterproof surface can delay the penetration of water into the textile structure.
• Helps maintain appearance: Water can cause visible discoloration, staining, or localized discoloration on some textile surfaces. Good water resistance helps reduce these effects.
• It facilitates easier cleaning: When water and liquid contaminants remain on the surface of the fabric instead of penetrating it immediately, they are potentially easier to clean.
• It supports material durability: Repeated exposure to moisture can contribute to undesirable changes in the appearance and performance of textiles. Therefore, waterproofing can be an element of an overall durability strategy.
• It supports consistent supplier quality: A standardized testing method allows textile suppliers and laboratories to evaluate materials using a common procedure, rather than relying solely on subjective descriptions such as water resistance.

The GMW 4726 standard applies to textile materials used in automotive applications, including:

• Upholstery fabrics
• Upholstery textiles
• Door panel textiles
• Ceiling fabrics
• Interior trim textiles
• Other textile-covered interior components

Water repellency testing, along with tensile strength, tear strength, elasticity and durability, flammability, abrasion, friction, dimensional stability, and seam fatigue tests, are included in textile laboratory qualification programs.

The GMW 4726 standard should not be confused with many other common automotive textile tests. These standards and the main characteristics evaluated are as follows:

• GMW 4217 Dimensional Stability
• GMW 3326 Trapezoidal tear strength
• GMW 3405 Stitch fatigue
• GMW 3414 Artificial weather resistance
• GMW 3232 Flammability
• GMW 3208 Wear Resistance
• GMW 4090 Weave / yarn number

These tests complement each other. For example, a textile might have excellent abrasion resistance but still need a separate assessment for waterproofing.

In conclusion, the GMW 4726 standard defines a test method used to evaluate the water resistance of automotive textile surfaces. This standard involves a controlled spray test followed by a visual assessment of the textile surface.

This test is particularly useful for verifying the consistency of waterproofing processes and the performance of automotive upholstery and interior textiles. The results can help automotive manufacturers and suppliers check material quality, appearance, and resistance to liquid exposure.

For laboratory proficiency testing or production approval, the latest version of the current standard should always be used, including specified sample preparation, conditioning, spraying parameters, evaluation criteria, and acceptance requirements.

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 in accordance with the GMW 4726 standard.