The objective of this work was to evaluate the effects of CaO-based particle film on the physiological parameters of cowpea (Vigna unguiculata) subjected to water restriction. Plants were subjected to two levels of soil moisture and three concentrations of the film, as follows: control, without film + 100% crop evapotranspiration (ETc); without film + 50% ETc; 5% CaO + 50% ETc; 10% CaO + 50% ETc; 5% CaO + 100% ETc; and 10% CaO + 100% ETc. Plants treated with 50% ETc remained stable with the application of 10% CaO particle film and showed high photosynthetic assimilation of CO2 (32 μmol m-2 s-1), moderate transpiration (5.6 mmol m-2 s-1), maintenance of chlorophyll content, and greater intrinsic water-use efficiency (IWUE, 226.65 μmol mol-1) and instantaneous water-use efficiency (6.06 μmol mmol-1) than plants of the other treatments. Control plants and plants at 5% CaO + 50% ETc showed, respectively, photosynthetic assimilation of CO2 at 15.34 and 15.94 μmol m-2 s-1, transpiration at 3.51 and 3.45 mmol m-2 s-1, and IWUE at 177.7 and 198.9 μmol mol-1. The CaO-based particle film is effective in protecting bean plants subjected to water restriction.