Infant dysphagia is commonly managed using thickened formulas. Substantial research investigates thickening of a variety of beverages for adults and children, yet few studies address the unique considerations of thickened formula for infants. Understanding the consistency and behaviour of thickened formula will guide clinicians and parents to make informed decisions to minimise risk of aspiration. To investigate the effect of time and storage temperature on the flow properties of thickened formula, four formulas and two thickeners currently utilised at a major metropolitan children’s hospital in Australia were tested in combinations, at refrigerated and room temperatures. Their flow properties were measured at three time-points (baseline, 1 h, 24 h) using the International Dysphagia Diet Standardisation Initiative (IDDSI) Flow Test, the current clinical standard for classifying drinks based on flow properties. A combination of paired t tests, Wilcoxon Signed-Rank tests, repeated measures analysis of variance (ANOVA) and Cohen’s d was used to statistically compare flow properties and determine the significance of the observed data. At baseline, 98% (n = 48) of the thickened formula bottles were measured as thinner than the “mildly thick” IDDSI category to which they were prepared. Conversely, at 24 h, 17% were measured thicker than “mildly thick” whilst 10% measured too thin for the category “mildly thick”. Refrigerated samples increased in thickness more significantly over time compared to those stored at room temperature. Two of the formulas, when thickened, resulted in a foamy mixture non-compatible with IDDSI Flow Test measurement. As a result, these two formulas were not subjected to further testing. All the tested commercial products behaved differently to each other and were unstable over varying times and temperatures. This finding indicates the need for improved guidelines regarding preparation and storage of thickened fluids. Further investigation is recommended into the chemical processes underlying the observed deviations.