Considering the above-factors, the foam samples were prepared as cubes about 50 ± 1 mm on a side, placed in the beakers full of water. The beakers were sealed by plastic wrap and placed at an incubator at 70 °C from 1 to 7 days. Then the samples were dried at 100 °C to constant weight. The durability was characterized by the mass loss calculated using the difference in weight before and after the test. Fig. 5 shows that the mass loss is still less than 2.4 wt.% after 7 days, which indicates that the foam has an excellent durability.