A method of measuring polymer foam expansion comprising extruding a free foaming polymer formulation which comprises one or more blowing agents; feeding the extruded formulation through a right angle die to produce a formed foam having a foam front at an exit of the die; measuring a thickness of the formed foam at the die nozzle, using a laser thickness measuring device comprising a laser, a vertical positioner driven by a motor drive wherein the laser is attached to the vertical positioner permitting adjustment of a vertical position of the laser; adjusting a speed of the motor drive so that the laser moves at a vertical displacement rate equal to the vertical displacement rate of the foam front exiting the die; and recording the foam thickness, wherein the thickness of the formed foam is measured every x seconds where x is from 0.05 to 0.15 and the thickness is recorded as a function of time is provided. Also provided is an apparatus for executing the inventive method.