Abstract The water absorption characteristics of pineapple leaf fiber (PALF)/glass fiber (GF) hybrid polyester(PER) composites, and chemically modified PALF/polyester composites were evaluated by immersion in distilled water at 28, 60, and 90°C. The diffusion properties of the intimately mixed (IM) and the layered hybrid composite GPG (Glass skin and PALF core) of different PALF/GF ratio at the three temperatures were compared in order to identify the environmental ageing mechanism at different temperatures. The effect of temperature on the kinetics and thermodynamics of diffusion were also examined. The water uptake of both IM and GPG hybrid composites was decreased with increase in glass fiber content; the lowest water uptake was observed for 0.46 V f GF hybrid composite. Among the chemically modified composites, vinyl tri 2‐methoxy ethoxy silane treated composites showed the lowest water uptake. Finally, parameters like diffusion, sorption, and permeability coefficients were determined. It was observed that equilibrium water uptake is dependent on the nature of the composite and temperature. Experimental results were also compared with theoretical predictions. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers