Abstract: Shown is an apparatus and method of use where microwaves transmitted through volatiles include water vapor driven from an adequate polymer sample by heating in a closed test cell. A pump moves a predried gas and those volatiles at pressure and flow rate to a microwave transducer including a pair of antennae horns aimed at one another, one with a microwave transmitter oscillator and the other with a receiver detector. The volatiles are brought transversely across the open end of the oscillator antenna horn by a conduit. The particular orientation of the conduit is important to the accuracy of the measurement. A moisture absorbent material inserted axially into the conduit restrains the flow of volatiles changing same to liquid form. Loss of microwave energy due to the water vapors in the volatiles is measured at the output of the detector. Microwave energy absorbent material surrounds the transducer.