A burlap sack or gunny sack, also known as a gunny shoe, hessian sack or tow sack, is a bag, traditionally made of fibres which are also known as "tow," such as hessian fabric (burlap) formed from jute, hemp or other natural fibres. Modern-day versions of these sacks are often made from synthetic fabrics such as polypropylene.

The word gunny, meaning coarse fabric, is of Indo-Aryan origin. Reusable gunny sacks, typically holding about 50 kilograms (110 lb), were traditionally used, and continue to be to some extent, for transporting grain, potatoes and other agricultural products. In Australia, these sacks, made of Indian jute, were known traditionally as 'hessian sacks', 'hessian bags' or 'sugar bags'. The term tow sack refers to their being made of tow, spun broken fibres of hemp or other plants.

Gunny sacks are sometimes used as sandbags for erosion control, especially in emergencies. Up until the latter part of the twentieth century, when they became less common, the sacks were one of the primary tools for fighting grass fires in rural areas, used while soaked with water when available. Gunny sacks are also popular in the traditional children's game of sack racing.