Friction and slip performance testing measures the static and kinetic coefficients of friction between contacting surfaces, providing essential data for packaging machinability, pedestrian safety, and product design. This article explains the testing principles, applicable standards such as ISO 8295, ASTM D1894, and GB/T 10006, typical sample types, test methods, and industrial applications. It also answers frequently asked questions to help manufacturers interpret results and control the surface friction characteristics of their materials.
Technical Overview
Friction and slip performance testing evaluates the resistance to relative sliding between two surfaces in contact under a defined normal load. Results are expressed as dimensionless coefficients: the static coefficient of friction, which characterizes the force required to initiate motion, and the kinetic coefficient of friction, which characterizes the force required to sustain motion at a constant speed. For most material pairs the static value exceeds the kinetic value, and both directly influence how films feed through converting lines, how packages stack and transport, and how safely pedestrians walk on finished surfaces.
The fundamental relationship is simple: the coefficient of friction equals the measured friction force divided by the normal force. In practice, a calibrated force-measuring system records the drag force acting on a standardized sled, and the coefficient is calculated by dividing that force by the sled weight acting as the normal load. Testing is typically performed by accredited third-party laboratories using dedicated coefficient-of-friction testers or universal testing machines equipped with low-friction sled fixtures, in accordance with internationally recognized standards.
- ISO 8295 — Plastics: film and sheeting, determination of the coefficients of friction
- ASTM D1894 — Static and kinetic coefficients of friction of plastic film and sheeting
- GB/T 10006 — Determination of friction coefficients of plastic film and sheeting, technically aligned with ISO 8295
- ASTM D4917 and ASTM D4918 — Horizontal plane and inclined plane methods for uncoated paper
- EN 13036-4 — Pendulum slip resistance test method for surfaces
- DIN 51130 and DIN 51097 — Ramp test classifications for shod and barefoot pedestrian floor slip resistance
Testing Samples
Plastic Films and Flexible Packaging Laminates
PE, PP, BOPP, CPP, PET, and PA films, as well as multilayer laminates used for bags, pouches, labels, and overwraps. Both film-to-film and film-to-stainless-steel contact configurations are commonly evaluated, because the contact surfaces of packaging machinery are usually polished metal.
Paper and Paperboard
Uncoated and coated printing papers, kraft sack paper, carton board, and corrugated liners. Friction behavior governs sheet feeding in printing and converting lines and the stacking stability of filled paper sacks.
Rubber, Elastomers, and Polymer Products
Sheets, seals, gaskets, conveyor belts, tubing, footwear outsoles, and glove materials for which grip, anti-slip behavior, or controlled lubricity must be quantified.
Flooring and Architectural Surfaces
Ceramic and porcelain tiles, natural stone, wood and laminate flooring, resilient flooring, surface coatings, and anti-slip treatments assessed for pedestrian safety under dry, wet, or contaminated conditions.
Metal Sheets and Coated Components
Pre-painted or lubricated metal sheets for deep drawing, anodized or powder-coated panels, and engineering sliding pairs where friction affects forming quality, assembly behavior, and long-term service performance.
Textiles and Nonwovens
Hygiene nonwovens, technical textiles, and interlinings, where surface friction influences web handling, converting efficiency, drape, and end-use comfort.
Testing Items
Depending on the product specification and intended service environment, friction and slip performance testing may include the following measurable items:
- Static coefficient of friction — the ratio of the peak initiating force to the normal force
- Kinetic (dynamic) coefficient of friction — the ratio of the average sustaining force to the normal force
- Slip angle on an inclined plane, whose tangent equals the static coefficient of friction
- Pendulum test value and slip resistance classification for pedestrian walking surfaces
- Friction behavior as a function of temperature, humidity, contact pressure, dwell time, and repeated sliding cycles
- Coefficient stability after thermal aging, surface treatment, sterilization, or migration of slip agents
Testing Methods
Horizontal Plane (Sled) Method
This is the most widely used procedure, described in ISO 8295, ASTM D1894, and GB/T 10006. A flat specimen is secured to a horizontal stage, and a sled faced with a second specimen or a standard reference surface, with a defined mass commonly of 200 g, is placed on top. The sled is drawn at a constant speed, typically between 90 and 150 mm/min depending on the standard, while a force sensor records the resistance. The first force peak yields the static coefficient, and the mean force during steady sliding yields the kinetic coefficient. Testing may be conducted film-to-film or film-to-metal, and both machine direction and transverse direction orientations should be assessed for anisotropic materials.
Inclined Plane Method
One surface is fixed to a slowly tilting plane while a slider faced with the counter-material rests upon it. The plane is raised at a controlled rate until sliding begins, and the tangent of the tilt angle at that moment is reported as the static coefficient of friction, often expressed directly as the slip angle. The method, covered by ASTM D4918 for paper, is particularly suitable for lightweight and flexible materials where sled inertia and system friction can distort horizontal plane results.
Pendulum and Ramp Methods for Pedestrian Surfaces
For flooring products, slip resistance is commonly measured with a pendulum friction tester in accordance with EN 13036-4, in which a spring-loaded rubber slider swings across a wetted surface and the energy loss is reported as a pendulum test value. Alternatively, ramp tests assess a walking operator on an inclined contaminated surface; DIN 51130 assigns shod classifications from R9 to R13, and DIN 51097 assigns barefoot classifications A, B, and C for wet areas such as pools and showers.
Specimen Preparation and Conditioning
Specimens must be cut flat and free of wrinkles, creases, and surface contamination, and the test surfaces should not be touched by hand before measurement. Conditioning is performed in a standard laboratory atmosphere, typically 23 °C ± 2 °C and 50 % ± 10 % relative humidity in accordance with ISO 291, unless the product specification requires other conditions such as elevated temperature or dry state. Multiple replicates, commonly at least three to five per condition, are tested and the mean values are reported together with the test direction, contact configuration, and environmental conditions.
Applications
Friction and slip performance data support design decisions, process optimization, and compliance demonstration across a broad range of industries.
- Flexible packaging and converting: verifying film machinability on form-fill-seal and bag-making lines, where kinetic coefficients of roughly 0.2 to 0.3 against metal are often targeted for high-speed operation
- Palletizing and transport: confirming adequate film-to-film friction for stack stability of bags, pouches, and cartons during handling and shipment
- Flooring and building products: demonstrating slip resistance classifications for entrances, corridors, wet rooms, and public facilities
- Automotive and general engineering: evaluating seals, sliding components, interior grip surfaces, and forming lubricants for metal sheets
- Structural engineering: characterizing friction sliding isolation bearings and energy-dissipating devices, where the effective friction coefficient and hysteresis behavior under cyclic loading directly affect seismic response
- Hygiene and medical products: optimizing nonwoven web handling, material drape, and glove or surface grip performance
- Quality control: incoming material inspection, slip agent and additive migration studies, and post-aging verification of surface properties
FAQ
What is the difference between static and kinetic coefficients of friction?
The static coefficient describes the resistance at the moment motion begins and is calculated from the peak initiating force. The kinetic coefficient describes the resistance during continuous sliding and is calculated from the average force at constant speed. Static values are normally equal to or higher than kinetic values, and both are needed to fully describe machinability and handling behavior.
Which standard should be selected for plastic film testing?
ISO 8295 and GB/T 10006 are widely used in Europe and Asia, while ASTM D1894 is common in North America. The methods are conceptually identical but differ in details such as sled geometry, sliding speed, and specimen dimensions, so results may not be directly interchangeable. The chosen method should always be stated in the test report.
What coefficient of friction values are suitable for packaging films?
For high-speed automatic packaging lines, a kinetic coefficient against metal of approximately 0.2 to 0.3 is often preferred. Values that are too high cause film jams and poor feeding, while values that are too low can lead to unstable stacks and slipping on conveyors. Acceptable limits should always be agreed between material suppliers and converters based on the actual equipment.
Do temperature and humidity affect the results?
Yes, significantly. Slip and antistatic additives migrate within polyolefin films as temperature changes, and coefficients measured at elevated temperature can differ markedly from room-temperature values. Humidity also affects paper, textiles, and coated surfaces. Specimens must therefore be conditioned in a controlled atmosphere before testing, and special-condition testing should be specified when the product will see hot filling, tropical climates, or cold-chain storage.
Can testing be performed on finished products rather than raw material samples?
Yes. Specimens can usually be cut from finished bags, pouches, tiles, sheets, or assemblies, which is useful for verifying the effect of printing, lamination, coating, or surface treatment. Care must be taken that the sampled area is flat, undamaged, and representative of the entire product batch.
