This SAE Recommended Practice describes a laboratory test procedure for evaluating the loss of thickness and the amount of structural breakdown of slab polyurethane foam seating materials. A test specimen is measured for thickness under a specified load and subsequently subjected simultaneously to compressive and shear deformation in a controlled atmosphere. This is accomplished by subjecting the foam to a rolling shearing action under a constant load for a specified number of cycles. Specimen thickness under a constant load is obtained after a 1 hr recovery period following dynamic fatigue to determine loss in foam thickness.