For many decades lagging has been used to both protect conveyor pulleys and to increase the available friction for driving the conveyor belt. Today lagging is available in various designs with differing stated capabilities and strengths.
A primary consideration in the choice of lagging is the coefficient of friction. Designers use the friction coefficient in the pulley wrap factor equation to calculate the drive capacity of the conveyor, so the behaviour of lagging friction under real world conditions is of extreme interest. As belt technology innovates with increasing tensions and more power delivered through the drive pulleys, a correct understanding of the source of friction is necessary.