The R-value says something about the anti-slip value of a floor tile and therefore the amount of grip a tile has. The values you use range from 8 to 12 with 8 being the lowest value. The higher the value, the more grip the tile has. R9 is the standard slip resistance value for ceramic floor tiles. Tiles with a higher R-value are recommended, especially in damp or greasy areas. Consider, for example, a butcher's shop.
Origin of our hair
The R-value was devised in Germany and is determined according to the 'Schiefe Ebene (slant slope) method'. The R stands for the German word 'rutsch', which means 'slipping'. In this method, the tile rests on a plateau that can be set to different angles of inclination. A test subject with appropriate shoes then stands on the tile. The angle of inclination is increased step by step until the person slips. Curious how they perform this test? Watch the video below.
3° and < 10° Dry areas R9 / R10
10° and <19° Kitchens, fresh shops R11
19° and < 27° Kitchens, wet areas such as showers and spas R12
27° and < 35° Whole wet production areas > R12
> 35° Very wet and greasy areas, such as a butcher's shop > R12 / R13
Video R-value test
Watch a video here in which they examine the R-value of a tile.