Mercury porosimetry can be used to characterize the structure of magnetic tape coatings but to get accurate information, compressibility corrections for the sample cell and basefilm must be made. Equations to make these corrections have been developed and published previously. These equations have been used to help interpret recent studies of tape coatings. These analyses have shown: 1. The Critical Pigment Volume Concentration (CPVC) of a magnetic pigment can be determined by measuring the mercury porosity of actual magnetic tapes. This CPVC can differ from the CPVC determined from tensile measurements of thick uncalendered coatings. 2. Postcuring of magnetic metal powder coatings was followed by measuring porosity and compressibility with mercury intrusion. The curing with isocyanate follows a first order reaction kinetics and is a relatively slow process, even after 7 days of storage the coating is not fully cured. 3. Multipass durability of (metal powder) audio tapes is directly correlated with porosity of the coating layer. For durable tapes porosity must be absent.