AbstractRigid polyurethane (PUR) foam is one of the most important insulating materials used today in the construction industry and is the main insulation material used in the global appliances industry. This study developed rice straw fiber-filled PUF (RPUF) and wheat straw fiber-filled PUF (WPUF) and explored the morphology, sound absorption properties, heat transfer, and compressive strength of the PUF composites. The results indicated that, with the higher fiber content, more open cells were observed in SEM images of the composites. The average sound absorption coefficients (ASAC) of both WPUF and RPUF were significantly increased when 5 per hundred polyols (php) by weight and 10 php fiber contents were added. When fiber contents of 15 php and 20 php were utilized, ASAC reduced due to the tortuosity of cells and large holes in the foam. The sound absorption coefficient (SAC) first increased, then decreased, and increased finally as the sound frequency increased from 100 to 2000 Hz for the two composites. The thermal conductivities of both WPUF and RPUF first decreased and then increased as the fiber content increased from 0 to 20 php. When 5 and 10 php straw contents was added, the thermal conductivities were reduced by 25% to 50% compared to that of the pure PU form (0 php), indicating that the improved thermal insulation ability was obtained. The composite compressive strength was reduced by 19% to 28% due to the fiber addition.