Yarn bombing, (also known as yarnbombing, yarnstorming, guerrilla knitting, urban knitting or graffiti knitting) is a type of graffiti or street art that employs colorful displays of knitted or crocheted yarn or fibre rather than paint or chalk.
While yarn installations – called yarn bombs or yarnstorms – may last for years, they are considered non-permanent, and, unlike other forms of graffiti, can be easily removed if necessary. Nonetheless, the practice is still technically illegal, though it is not often prosecuted vigorously.
While other forms of graffiti may be expressive, decorative, territorial, socio-political commentary, advertising or vandalism, yarn bombing was initially almost exclusively about reclaiming and personalizing sterile or cold public places. It has since developed with groups graffiti knitting and crocheting worldwide, each with their own agendas and public graffiti knitting projects being run.