Mummified animal skin with tar content from the castle of the late medieval town of Novo Brdo (Central Balkans)

•Novo Brdo was an important late medieval mining center of the Balkans and Europe.•Unique assemblage of animal skins with preserved hair and filled with resin was discovered.•The light and SEM microscopy analysis of hair microstructure and FTIR of resin was performed.•The skins originated from goat and sheep, and the resin was identified as pine tar.•The tar stored in the skin was most likely used for the impregnation of wooden structures.