In the present work, poly(vinyl formal) (PVF) foams were prepared using water as the pore-forming agent and formaldehyde as the crosslinking agent. The acetalization process of poly(vinyl alcohol) was exploited in depth in order to obtain a precise guidance on the preparation of PVF foams with adjustable properties. With the increasing of formaldehyde, the crosslinking degree was gradually increased and the prepared PVF foams changed to be amorphous. Morphology observation showed that the porous structure of PVF foams was successfully created using water as the blowing agent and it was strongly affected by the crosslinking agent and polymer concentration, leading to an easily tuned pore size from hundreds of microns to few microns. The prepared foams were proved to have small apparent density below 0.27 g/cm(-3)and excellent mechanical strength, with the largest specific compressive strength of 11.54 MPa center dot cm(3)center dot g(-1). Based on the results, it is believed that this study can provide a scientific basis for the design and optimization of PVF foams with controllable structure and properties.