The slipperiness of a floor relates to how safe it is to walk on and, for this reason, is a fundamental feature of the floor itself.
Slipperiness is indicated by the R-value, which refers to a method required by the German DIN 51130 and 51097 standards, which classify products based on their coefficient of friction, as a function of the specific needs of a certain space.
Depending on the level of slipperiness, which could be linked to the use of specific substances in certain work areas, or the presence of water, the standards require the use of flooring materials capable of creating a significant level of friction between contact surfaces to limit its danger for people.
The greater the coefficient of friction, the lower its slipperiness. The standard distinguishes the slipperiness of treadable surfaces between areas where one walks wearing shoes (R9-R13) and those where one walks barefoot (A, B and C).

The measurement method required by the DIN 51130 standard defines the following slipperiness classes and indicates their respective environments of use:
• R9 – entrance areas and stairs with access to the outside, restaurants and cafeterias, stores, clinics, hospitals and schools.
• R10 – common bathrooms and showers, small kitchens in foodservice businesses, garages and cellars.
• R11 – food-production areas, medium-sized kitchens in foodservice businesses, processing environments with a high presence of water and sludge, workshops, laundries and hangars.
• R12 – areas for the production of fatty foods such as dairy products and derivatives, oils and deli meats, large kitchens in foodservice businesses, industrial departments where slippery substances are used and parking lots.
• R13 – areas with large quantities of fats and food processing.

For wet areas where people will be walking barefoot, the floor must meet even stricter requirements.
These can be measured based on the DIN 51097 standard and are classed in groups A, B, C with increasing values:
• A – locker rooms, areas where people go barefoot, etc.
• B – showers, swimming pool sides, etc.
• C – sloping swimming pool sides, submerged ladders, etc.