Sandbag construction is a centuries old technique that has changed little. Sand bags are made from different materials, the most common being hessian. More recently woven polypropylene sandbags have been introduced and are proving more effective for certain operations involving these flood defence sandbags.

Sand is by far the easiest and most effective material for filling and shaping sandbags. In a time of flooding the rain also helps to saturate from the rain and also makes the bags heavier. During emergencies, sand may not be available and so silt, clay, gravel or a mixture of these may be used, but none work as well as sand. Sometimes during a flood there may be no vehicle access to a flood site, and this is when materials other than sand may be used.

Sandbags can be used to:

- Prevent overtopping levees

- Direct a river's current flow to a specific are

- Construct ring dikes around boils on a levee

- Use as a weight for holding down traffic signs for example

- Stacking sandbags by home gates and doors can greatly diminish flood damage

It is commonly thought that sandbags should be built as a wall to completely block water, this is a misunderstanding. It is possible to completely block water, but this requires enough time to construct a pyramid styled wall many sandbags thick. This takes time and the very nature of flooding means that people rarely have time to prepare. The force of the water can be so great it is much more advisable to quickly build a much thinner wall with the aim of redirecting the flow of the water away from the location being targeted by the water flow. Using this method gives you a much greater chance of preventing flood damage to your property as opposed to attempting to build a blocking wall, which will probably get washed away.

The flow of water is greatly underestimated, people trying to block will probably be happy with how it goes to start with, but if the water has nowhere to go, it will build up, rise and rise. The great build of force will mean the water will start finding gaps in the sandbags and also moving some of the bags out of place and if you do not keep building the wall higher, the water will very surely overflow your wall and surge into your property causing painful damage.

If you live in a flood risk area or feel that there is a probability of your home or property being flooded it is highly recommended to keep some sandbags in your garage or the downstairs of your home.