The aim of this work to explore the absorption behavior of bio composites reinforced with date palm fibers. RSM and ANOVA were utilized to evaluate the impact and interdependence of input variables (Time: from 24 h to 672 h, Fiber content: 15 %, 20 %, and 25 %, and types of water: seawater, distilled water, and rainwater) on the output variables (Mass of CDPF) during a water absorption process that lasted more than 670 h at 23 °C. The findings revealed that the bio composites with the above-mentioned filler content absorbed more water as the amount of fibers increased, with absorption rates of 14.03 %, 19.39 %, 30.94 % for seawater, 15.42 %, 20.64 %, and 36.08 % for distilled water, and 16.37 %, 21.98 %, and 42.10 % for rainwater, respectively. Additionally, the study measured the diffusion coefficient of bio composites, which had a minimum value of about 2.11 × 10−6mm2/s and a maximum value of about 3.99 × 10−6mm2/s. The results of RSM model analysis showed that this model is accurate and reliable. Where the values of R2 and adjusted R2 coefficients for the Mass of CDPF were 99.63 % and 99.61 %, respectively, indicating an ideal match between experimental and predicted values. These findings provide valuable information for engineers interested in incorporating date palm fiber bio composites during development and implementation.