Footwear Slip Resistance: Comprehensive Analysis of Characteristic Indicators and Testing

Slips, trips, and falls are recognized as a leading cause of accidents in workplaces, public spaces, and home environments. Consequently, the slip resistance of footwear has become critically important. This article compiles information on testing methods and influencing factors related to shoe slip resistance.

Common sense tells us that sliding occurs between two objects when their mutual friction force is less than the external driving force. If the friction force between the shoe and the ground exceeds the tangential component generated during walking, it is sufficient to prevent the shoe from sliding, thereby eliminating or significantly reducing the likelihood of slips and falls. Therefore, friction force is the key factor determining whether slippage occurs between the shoe and the ground.

Quantified through two metrics:

Coefficient of Friction (COF)

Divided into static friction coefficient (μs, static slip resistance limit) and kinetic friction coefficient (μk, stability during sliding). Generally, μ ≥ 0.4 is required for safety on wet/slippery surfaces, with higher requirements in greasy kitchen environments.

Critical Tilt Angle (CTA)

The platform tilt angle at which the sole begins to slip; a larger angle indicates superior slip resistance. EN ISO 13287 mandates a wet CTA ≥8°, while DIN 51130 classifies Grade A slip resistance as the optimal level for oily surfaces.

Test Logic: Place the shoe sample on an adjustable-angle platform (covered with standard surfaces like ceramic tiles or oil-coated steel plates), gradually increase the incline until slippage occurs, and record the critical angle. This directly simulates the slip resistance limit during walking and is suitable for testing safety shoes and outdoor boots.

Core Equipment: Tilting slip resistance platform (accuracy ±0.1°, load capacity 50-100kg).

2.2 Coefficient of Friction Test Method (Instrumental Method)

Standards: ASTM F2913, GB/T 3903.6-2024

Test Logic: Based on Coulomb's Law (μ=F/N), friction force and vertical pressure are measured via sensors. Pendulum-type instruments measure dynamic friction, while traction-type instruments simulate gait speeds (0.3m/s±0.02m/s).

2.3 Scenario Simulation Testing

For specialized footwear customization—e.g., dynamic gravel testing for hiking boots or cooking oil surface validation for kitchen shoes—a six-degree-of-freedom mechanical leg replicates real gait patterns. High-speed cameras analyze sliding trajectories.

3.1 Select appropriate test lasts and insert them into the shoes;

3.2 Choose corresponding test media and interfaces based on footwear type or usage scenarios;

3.3 Select the test mode based on the test objective or product standard requirements;

3.4 Mount the test specimen onto the testing instrument fixture;

3.5 Apply the specified load to the specimen within 0.2 seconds before sliding and conduct the test at the prescribed speed. Record all friction forces between 0.3 and 0.6 seconds after sliding commences, then calculate the specimen's coefficient of friction.

4.1Increasing friction between the outsole and ground surface is the primary method to improve shoe slip resistance, with enhancing the outsole material's coefficient of friction being the key factor. Improvements can be achieved through material selection, tread patterns, and groove depth.

4.2Current outsole materials include rubber, PU, EVA, PVC, SSBR, natural leather, and TPU. Among these, rubber is widely recognized as one of the best materials for slip resistance.

4.3Within the same material, altering the outsole's structural design can enhance its grip on surfaces, significantly boosting slip resistance. For instance, avoiding smooth, rigid soles and opting for textured, patterned, or grooved structures is beneficial. Furthermore, different outsole designs exhibit varying friction and grip levels when paired with different surfaces.

4.4Furthermore, specific requirements exist for the pattern layout and depth on shoe outsoles. Generally, patterns should be concentrated on the forefoot and heel contact areas, featuring a diagonal design. When pattern depth exceeds 2.5mm, the shoe achieves superior slip resistance.