We investigated an unusual ice type, called hair ice. It grows on the surface of dead wood of broad-leaf trees at temperatures slightly below 0°C. We describe this phenomenon and present our biological, physical, and chemical investigations to gain insight in the properties and processes related to hair ice: we found, that a winter-acive fungus in the wood is required. Ice segregation is the common mechanism. Chemical analyses show a complex mixture of several thousand lignin/tannin compounds.