An Earthship is a type of passive solar house made of natural and recycled materials. Designed and marketed by Earthship Biotecture of Taos, New Mexico, the homes are primarily constructed to work autonomously and are generally made of earth-filled tires, using thermal mass construction to naturally regulate indoor temperature. They also usually have their own special natural ventilation system. Earthships are generally off-the-grid homes, minimizing their reliance on public utilities and fossil fuels. The Earthship Biotecture website states 'An Earthship is a radically sustainable green building made with recycled materials.'