Technical Abstract: Two major requirements that continue to hinder commercialization of numerous potential biopesticides are suitable shelf-life and reliable efficacy. Both formulation characteristics are affected by water availability; therefore investigating water-formulation interactions could provide insight into how both properties could be optimized. In the present study, three clay based biopesticides delivery systems, denoted as TRE-G, PEC-G and PESTA, were analyzed using a dynamic vapor sorption analyzer. The objective was to investigate the interaction of water with three different formulations at 25'C and to determine differences in water uptake and water loss kinetics in response to changes in ambient relative humidity over the range from 0 to 90%. All three formulations showed a similar sorption mechanism and no morphological change in response to rehydration. However, the formulations differed in water uptake capacities, rehydration and dehydration kinetics. Water vapor uptake capacity ranged from 5 to 12.5% w/w with TRE-G being the least absorptive and Pesta being the most. The Pesta formulation required 24h to rehydrate from a water activity of 0.10 to 0.70, while PEC-G and TRE-G required 12 and 14h, respectively. The time required for rehydration from a water activity =0.40 to 0.90 ranged from 8 – 32 h. The formulation response time to a decrease in relative humidity from 90 to 70% obeyed the following order: TRE-G < PEC-G < Pesta, with Pesta being the slowest. The implications of the findings as they relate to shelf-life and dew period requirements of biopesticides are discussed.