Liquefaction of the bark of Acacia mearnsii (BK) and cornstarch (CS) was conducted by using a solvent mixture consisting of poly(propylene glycol) (PPG), glycerol, and sulfuric acid with a weight fraction of 94/5/1 at 150 degrees C. Solubilities of BK and CS were about 80% after 60 min and 100% after 20 min in the same solvent, respectively. Highly elastic or highly resilient (HR) polyurethane foams (PUFs) suitable for car-seat cushions were prepared from the liquefied BK and CS without removing the insoluble residue from the liquefaction mixture. About 20% of the insoluble residue from BK contributed remarkably to the improvement of flame resistance of the resulting PUFs. HR PUFs having better resilience properties were prepared using PPC of molecular weight around 4000, as compared with poly(ethylene glycol) having the same hydroxyl value. PUFs were synthesized from three BKs with different tannin contents, that is, BK0 (tannin: 0%), BK1 (tannin: 43%), and BK2 (tannin: 48.5%), to evaluate the effect of the tannin content on their performance of resilience. Both the resilience value and density of the PUFs increased with increasing BK content for all BK systems. BK2 was chosen to prepare PUFs in the further work. When CS replaced part of BK, the density and compressive strength of the PUFs decreased with an increasing cornstarch proportion, whereas the resilience value had its maximum value when the weight ratio of CS:BK was 1:1. The PUFs were, to some extent, biodegradable: The average weight loss of samples buried in soil for 6 months was 15.6 wt %.