The transverse compression behavior of Douglas-fir wood (Pseudotsuga menziesii) at high temperature (170 °C) and saturated steam conditions was studied and compared with previously reported compression behavior of hybrid poplar (Populus deltoides × Populus trichocarpa). The effect of the compression on the stress–strain response, non-linear strain function, and relative density change was examined by a modified Hooke’s law based on the load-compression behavior of flexible foams. Transverse compressive loading followed a typical stress–strain curve of wood. The compressive modulus of Douglas-fir was higher than hybrid poplar. The yield stress of Douglas-fir specimens was higher than yield stress of hybrid poplar specimens, while densification stress of both wood species was the same. The comparison of the non-linear strain function of Douglas-fir and hybrid poplar specimens revealed significant differences. The observed differences are assumed to be due to different cellular structure and chemical composition of softwoods versus hardwoods.