Foams can naturally occur, such as the head on a beer, or be created with purpose, like fire extinguishers. The range of physical properties available to foams have resulted in applications which can be based on their viscosity. With more rigid and self-supporting forms of foams being used as insulation or cushions, and foams that exhibit the ability to flow being used in the cosmetic industry as shampoos or makeup. Foams have also found biomedical applications in tissue engineering as scaffolds and biosensors.