We examined archival data of the Palomar Testbed Inteferometer (PTI) covering a sample of 85 Mira variable stars. The sample contains the three most common types: 65 oxygen-rich (M-type), 11 carbon-rich (C-type) and 9 of the intermediary S-type; Periods range from 150 to 600 days. The PTI database spans over nine years of data; up to 80 epochs for individual stars, spanning multiple pulsation cycles per star. These interferometric angular sizes, along with ancillary measures of distance and bolometric flux, can be used to determine linear size and effective temperature, respectively. Additionally, the PTI data can be divided into narrowband data across the K-band (2.0-2.4 µm), allowing separate analysis of spatially resolved continuum and prominent molecular-bandhead regions of these stars, which typically pulsate out of phase. In this poster we present preliminary results that show average sizes changes of 40% for the stellar radii and 44 % for the molecular envelopes.