Artificial, synthetic sponges are frequently made from polyurethane foam. Along with releasing ozone-depleting chemicals during manufacturing, polyurethane can also emit formaldehyde, other irritants and cancer-causing dioxins when incinerated. Sea sponges are not much of a better solution, environmentally. According to the Australian Marine Conservation Society, sea sponges are under threat of extinction for a variety of reasons including over-harvesting.