Full Description

This method describes the procedure for measuring bulking thickness and variations in tissue paper and tissue products.
This test method uses a relatively low-pressure 2 kPa (0.3 psi) because of the collapsible structure of tissue paper. TAPPI T 411 Thickness (caliper) of paper, paperboard, and combined board uses a relatively high-pressure 50 kPa (7.3 psi).

An essentially identical method is described in ISO 12625-3 Tissue paper and tissue products -- Part 3: Determination of thickness, bulking thickness and apparent bulk density.