This work assesses the post fabrication shrinkage of 3 styles of Aquaplast Slimline U-Frame thermoplastic masks: Aquaplast RT (Aqua S); Fibreplast (Aqua KS) which is similar to Aqua S, but contains Kevlar for improved rigidity and reduced shrinkage; and Aquaplast RT Variable Perf (Aqua YS) which is similar to Aqua S but excludes perforations along various bands for improved strength. Each mask was formed over the same rigid anthropomorphic head phantom. Immediately post-fabrication, each mask was remounted onto an optical bench, where sequences of profile photographs were acquired over the span of one week. Points marked near the forehead, nose, and chin were tracked to determine the deformation of the masks. Reproducibility of point position determination was within about 0.02 mm. After one week, all points translated primarily in the posterior direction due to mask shrinkage. Observed translations were largest for the Aqua S mask where points translated by 2.31±0.05mm on average. The Aqua YS mask yielded the smallest translations: 1.57±0.03mm, 1.20±0.03mm, and 1.54±0.03mm for points near the forehead, nose and chin respectively. The Aqua KS mask yielded somewhat greater translations: 1.57±0.02mm, 1.20±0.02mm and 1.54±0.02mm for the same respective points. Future work will characterize other mask models and measure the pressure exerted at select points by each mask on the phantom after shrinkage.