Used to define the relationship between the weight of the drillstring and the force required to strip the string into the well. Pipe light occurs when the force required to lower the string is greater than the weight of the string. In this case, the string has to be “snubbed” into the well. Pipe heavy occurs when the weight of the string is greater than the upward force acting on the string. In this case, the string can be “stripped” into the well.