What is COF?
Coefficient of friction (COF) is the measurement of a tile's frictional resistance, closely related to traction and slipperiness. Both static and dynamic measurements can be taken. Static coefficient of friction (SCOF) is the frictional resistance one pushes against when starting in motion. Dynamic coefficient of friction (DCOF) is the frictional resistance one pushes against when already in motion. For SCOF and DCOF, a slip occurs when pushing off with more force than the surface can resist. That can happen when the angle of the force changes (e.g., pushing off harder while pressing down less) or when the floor surface becomes more slippery than anticipated.
While many tile products still show a "COF" value, many manufacturers have stopped reporting coefficient of friction per the ASTM C1028 method because the standard for tile floors has changed. There is now a >0.42 requirement, measured per the DCOF AcuTest℠, for level interior tiles that will be walked on when wet.
Read more about static and dynamic coefficients of friction and the DCOF AcuTest here.