Dry and Wet Slip Resistance Value Testing: Principles, Standards, and Applications

Dry and wet slip resistance value testing measures the coefficient of friction (COF) of footwear, flooring, and other surface materials under both dry and contaminated conditions, providing objective data that predicts real-world slip-and-fall performance. By applying internationally recognized methods such as EN ISO 13287, ASTM F2913, and GB/T 3903.6, accredited third-party laboratories help manufacturers, specifiers, and safety engineers verify compliance, optimize product design, and reduce liability. This article explains the test principles, sample types, testing items, measurement procedures, and typical applications of dry-state and wet-state slip resistance evaluation.

Technical Overview

Slip resistance describes the ability of two contacting surfaces, typically a shoe outsole and a floor, to resist relative sliding under load. It is quantified by the coefficient of friction (COF, μ), defined as the ratio of the tangential friction force (F) resisting motion to the perpendicular normal force (N) pressing the surfaces together (μ = F/N). A higher COF indicates a lower probability of slipping.

• Static coefficient of friction (SCOF) — the friction ratio measured at the instant sliding begins, relevant to the initiation of a slip.
• Dynamic coefficient of friction (DCOF) — the friction ratio measured while sliding is in progress, relevant to whether a person can recover balance after a slip starts.
• Pendulum test value (PTV) — an energy-loss based slip resistance index obtained with a swinging rubber slider, widely used for pedestrian surfaces.

Dry-state testing characterizes the intrinsic friction between two clean, uncontaminated surfaces. Wet-state testing introduces controlled liquid contaminants, such as tap water, sodium lauryl sulfate (SLS) solution, glycerol, or lubricating oil, to simulate kitchens, bathrooms, swimming pool decks, food plants, and industrial floors. Because liquid films can reduce friction by more than half, and the majority of pedestrian slip accidents occur on wet or contaminated surfaces, wet-state results are usually the decisive acceptance criterion in product certification and specification.

Testing Samples

Footwear and Outsole Materials

Finished whole shoes are the primary sample type, including safety footwear, protective footwear, and occupational footwear covered by EN ISO 20345, EN ISO 20346, and EN ISO 20347, as well as sports shoes, hiking boots, and service shoes. Outsole compounds, rubber or thermoplastic polyurethane (TPU) sheets, and prototype tread plaques are also tested during formulation and pattern development.

Flooring and Rigid Surfaces

Ceramic and porcelain tiles, natural stone, polished concrete, engineered wood and laminate, vinyl flooring (LVT/SPC), rubber flooring, stair treads, gratings, and anti-slip mats are evaluated to support product classification, quality control, and project specification.

Coatings, Films, and Other Products

Anti-slip coatings, transparent films and tapes, floor polishes and maintenance finishes, vehicle pedal pads, crutch and walking-stick tips, and coated fabrics can all be assessed using suitably adapted dry and wet friction methods.

Samples should be drawn from representative production batches, conditioned at 23 ± 2 °C and 50 ± 5 % relative humidity, and supplied in sufficient quantity to allow replicate measurements on unused contact areas. Surfaces must be cleaned according to the standard protocol to remove dust, mold release agents, and packaging residues before testing.

Testing Items

Typical test items reported for dry-state and wet-state slip resistance evaluation include:

• Dry-state static coefficient of friction (SCOF, dry)
• Wet-state static coefficient of friction (SCOF, wet, with water or specified contaminant)
• Dry-state dynamic coefficient of friction (DCOF, dry)
• Wet-state dynamic coefficient of friction (DCOF, wet, with water, SLS solution, glycerol, or oil)
• Wet pendulum test value (PTV/BPN) for pedestrian and paving surfaces
• Ramp test classification (R9–R13 for shod walking; A–C for barefoot areas)
• Verification of footwear slip marking (SRA, SRB, or SRC claims)

Test reports normally present individual and mean COF values for each contact mode (forward heel slip, forward flat slip, backward heel slip), each test surface and contaminant combination, together with the conditioning atmosphere, instrument calibration status, and a clear statement of the applicable acceptance criteria.

Testing Methods

Whole-Shoe Slip Testing (EN ISO 13287, ASTM F2913, GB/T 3903.6)

The finished shoe, mounted on a standardized last, is loaded vertically against a motor-driven test platform while the horizontal friction force is recorded. In EN ISO 13287 and the technically aligned GB/T 3903.6, the vertical force is typically 500 ± 25 N with a sliding speed of 0.3 m/s, using two standard surface and contaminant combinations: a clay ceramic tile flooded with a dilute sodium lauryl sulfate solution, and a smooth steel plate flooded with glycerol. Contact geometries include forward heel slip, with the heel inclined at approximately 7°, and forward flat slip. ASTM F2913 follows a comparable whole-shoe principle and adds a backward heel slip mode, allowing dry, wet, and contaminant-specific evaluation on a range of floor surfaces. The COF is calculated from the mean horizontal force divided by the vertical force over the defined measurement window.

Sled-Type Static COF Testing (ASTM C1028, ASTM D2047, UL 410)

A weighted sled fitted with a standard contact face is drawn at constant velocity across the specimen, and the ratio of pull force to sled weight yields the static COF. ASTM C1028 is applied to ceramic and similar tiles in both dry and tap-water wet conditions; ASTM D2047 measures static COF of polish-coated flooring using a specialized static friction instrument; UL 410 provides acceptance criteria for slip-resistant floor surface materials and coatings.

Pendulum Testing (ASTM E303, EN 13036-4)

A spring-loaded arm carrying a standardized rubber slider sweeps across the wet surface, and the energy lost to friction is read as the pendulum test value, formerly the British pendulum number (BPN). The method is portable, suitable for laboratory and on-site use, and widely applied to pedestrian flooring, walkways, and road surfacing.

Dynamic COF for Resilient Flooring (EN 13893, JIS A 1454)

EN 13893 determines the dynamic coefficient of friction of resilient, laminate, and textile floor coverings, while JIS A 1454 provides a Japanese test method for the slip resistance of flooring materials, supporting regional market compliance.

Ramp Classification Testing

A test operator walks on the specimen, which is mounted on an adjustable incline under a continuous contaminant flow, oil for shod safety assessments and water for barefoot areas. The critical angle at which secure walking is no longer possible is converted into classification grades R9–R13 or A–C, which are commonly used in European flooring specification.

Key Test Conditions and Quality Controls

• Conditioning of footwear and flooring specimens at 23 ± 2 °C and 50 ± 5 % relative humidity prior to measurement.
• Preparation of fresh contaminant films for each individual measurement to ensure repeatability.
• Multiple replicate measurements, with each measurement taken on an unused area of the contact surface.
• Instrument verification against certified reference surfaces, plus regular calibration of force sensors, speed control, and slider condition.
• Strict adherence to heel contact angle, normal force, and sliding speed defined by the selected standard.

Applications

Dry and wet slip resistance value testing supports a wide range of commercial, regulatory, and engineering purposes:

• PPE certification: demonstrating SRA, SRB, or SRC slip performance for safety footwear under the EN ISO 20345 marking scheme, with type examination and ongoing verification performed by accredited third-party laboratories.
• Product development: optimizing outsole tread geometry, rubber compound hardness, filler loading, and surface micro-texture to improve wet grip without sacrificing wear resistance.
• Flooring specification and quality control: verifying declared slip classes for hospitals, airports, shopping malls, industrial plants, and swimming pool environments before and after installation.
• Occupational risk assessment: evaluating shoe–floor combinations for food processing, hospitality, healthcare, and oil and gas operations where liquid contamination is routine.
• Marketing claim substantiation: providing objective evidence for anti-slip claims on footwear, coatings, mats, and flooring products.
• Incident investigation: supplying technical data for expert analysis following slip-and-fall accidents and insurance or legal proceedings.

FAQ

What is the difference between dry-state and wet-state slip resistance testing?

Dry-state testing measures friction between clean, uncontaminated surfaces and reflects ideal conditions. Wet-state testing introduces water, detergent solutions, glycerol, or oil to reproduce realistic service conditions. Because most slip accidents happen on contaminated surfaces, wet-state results are generally the more meaningful and more demanding acceptance criterion, and values often drop by 30–70 % compared with dry measurements.

What slip resistance value is considered safe?

No single number applies to all methods. Commonly cited benchmarks include a static COF of 0.5 or higher under UL 410 and sled-type methods, a wet DCOF of 0.42 or higher for level interior floors referenced in North American tile specifications, a PTV of 36 or above generally regarded as low slip potential, and EN ISO 20345 thresholds of at least 0.32 on ceramic tile with SLS solution (SRA) and 0.18 on steel with glycerol (SRB). The intended use environment, contamination type, and maintenance regime must always be considered alongside the numeric result.

Which standard should my product be tested against?

Footwear should be evaluated using EN ISO 13287, ASTM F2913, or GB/T 3903.6 depending on the target market; rigid tiles are commonly assessed by ASTM C1028 or pendulum methods; resilient and textile floor coverings fall under EN 13893; pedestrian paving and road surfaces are tested per EN 13036-4. Regulated personal protective equipment must follow the slip marking scheme of the applicable EN ISO 20344/20345 series, verified through accredited third-party laboratories.

Why do products that pass dry testing sometimes fail wet testing?

Liquid films act as lubricants and can generate hydrodynamic pressure that separates the outsole from the floor. Smooth tread patterns lack drainage channels, polished or worn surfaces lose micro-texture, and hard compounds deform less, reducing true contact area. Wet testing with glycerol or SLS solution deliberately exposes these weaknesses, which is precisely why it is required for certification.

How can manufacturers improve wet slip resistance?

Effective strategies include designing tread channels and leading-edge grooves that displace liquid, selecting softer rubber compounds with higher hysteresis, incorporating silica-based fillers, and increasing surface micro-roughness. Improvements should be confirmed through iterative dry and wet slip testing at each design iteration rather than relying on dry-state results alone.