Flood control sandbags are generally made of canvas, the same material used in disaster relief tents. Furthermore, most waterproof tarpaulins used for moving and transporting carts are also made of canvas. Relatively speaking, canvas is quite sturdy and durable for construction.
The main material of canvas is cotton, meaning it is also susceptible to damage from sunlight and damp environments.
Basically, if flood control sandbags are piled up in a corner and left to deteriorate after use, they may become unusable after one or two years. However, if they are dried promptly after use and then stored in a dry, cool environment, they can last for four or five years without problems.
Of course, this refers to usage scenarios in residential areas, businesses, or street-front shops. Flood control sandbags used in emergency situations such as flood prevention and disaster relief are usually filled directly with soil. In this case, the sandbags are mostly for single use.