Wool is a natural fiber with the potential to be used in wearable RF devices or as a printed-circuit-board substrate reinforcement. Wool fibers are normally woven or entangled, and the resulting textile comprises a substantial amount of air. Therefore, the textile relative permittivity has a magnitude close to unity which is challenging to measure. In this work, a test fixture is described for measuring the permittivity of a wool-air mixture. It is based upon a low impedance inverted microstrip in which the air is replaced by the textile. Two different test fixture lengths are required for permittivity measurement using the through-line deembedding method.