FloodSax: How the Expanding Flood Bags Work and How to Use Them

FloodSax are lightweight bags that stay flat and dry on the shelf until you put them in water. Each one weighs just under 1lb (.37 kilos) before it comes into contact with water, and around 20kg once it has absorbed its full capacity of about 20 litres¹. For a household getting ready for a flood, that means a box you can carry with one hand becomes a stack of heavy, mouldable bags you can build into a barrier at a door, or drop down a toilet to stop sewer water coming back up.

The maker says a FloodSax expands in about five minutes when immersed in water in a bath, sink, bucket or even the floodwater itself¹. Each row of bags keeps around 18cms (7ins) of water out, so the number of rows you need depends on how deep water could get at your door¹. They are single use once activated, and the maker gives specific disposal instructions for after a flood.

This page covers what FloodSax are, how to activate and place them, how to store them so they are ready, and how to dispose of them safely. It is written for a household building a flood plan, alongside the wider Flooding: A Household Guide.

What FloodSax are and how they work

A FloodSax is a flat, fabric bag containing a gelling polymer and wood pulp. The maker describes each one as made up of 4 layers with 12 internal absorbent sections, creating a multi-chamber system to keep the water where it is put, sewn into an outer sleeve of nonwoven material¹. The inner material is mostly biodegradable, while the outer cover is a nylon polymer material with nylon stitching¹.

To activate one, immerse it in water in a bath, sink, bucket or the floodwater itself. The gelling polymer absorbs and retains the water, and the bag becomes taut and heavy enough to stack¹. The maker says they are designed so they mould into doorways to keep floodwater out¹.

For a household, the practical point is that FloodSax are a store-flat alternative to sandbags. They look a bit like pillowcases or empty sandbags until they come into contact with water, and are vacuum-packed and ultra thin with a large surface area³. FloodSax sit on a shelf until needed, then become the weight you need at the door.

Size and weight: about 20kg and 20 litres once expanded

The figures that decide how you use FloodSax are the ones before and after activation. Before activation, each bag measures 520mm (52cms) by 470mm (47cms) by 12mm (1.2cms) and weighs just under 1lb (.37 kilos), also stated as 13 ounces¹. After it has absorbed the water it will be about 170mm (17cms) deep and the same length and width¹.

The maker notes a manufacturing tolerance of plus or minus 20% in each FloodSax¹, so treat the 20kg and 20 litre figures as approximate. A pack of 5 will soak up to 100 litres of water¹. For storage planning, the maker says 24 boxes weighing 253kg can be stacked on a standard pallet, and a 40ft-high lorry container can take 1,496 boxes loose-packed or 1,120 on pallets¹, figures that matter to a group buying for a street or community store rather than a single home.

The weight once expanded is the figure to plan around. Around 20kg per bag is heavy enough that you want to build a barrier before water arrives, not while wading. Keep the box somewhere you can reach it without moving other stores, and think about who in the household can lift a 20kg bag safely.

How to activate FloodSax in about 5 minutes

Activation is simple, but the order matters when water is rising. The maker says a FloodSax expands in about five minutes once immersed¹. Work through it in this order:

1. Get the dry bags to the point where you need them before water reaches the door.
2. Fill a bath, sink or bucket, or use the floodwater itself, as the maker describes¹.
3. Immerse each bag and leave it for about five minutes until it is taut and heavy¹.
4. Stack the expanded bags into rows at the doorway, moulding them into the gap as the maker intends¹.
5. Keep the rest of the box dry and flat until you need the next row.

Building a barrier at a door: each row keeps out around 18cm of water

The maker states that each row of FloodSax will keep around 18cms (7ins) of water out¹. To plan a barrier, estimate the depth of water that could reach your door and allow one row for each 18cms. A doorstep that could see 50cms of water needs three rows by that measure.

Official guidance supports having barriers ready before a flood. The Northern Ireland Executive advises households to have some sandbags, floodboards, or plastic covers prepared to block doorways and airbricks⁴. Natural Resources Wales lists flood doors, air bricks and hydrosacks among the product examples households can use⁵. Westminster City Council advises residents to buy flood protection products and find service providers on the National Flood Forum's Blue Pages Directory, and to get ready with a supply of temporary flood barriers⁶.

FloodSax are one temporary barrier option among several. Official guidance describes resistance measures that can be installed to keep the water out, including flood doors, barriers, gates and walls⁷, and product types ranging from simple sandbags to water-resistant barriers and doors and special valves on drains⁸. FloodSax suit a household that wants something flat to store and quick to deploy; a fitted flood door or a permanent barrier suits a home that floods repeatedly. The Flooding: A Household Guide sets out the wider plan, including warnings and evacuation.

Blocking the toilet against sewer backflow

Sewer water coming back up through the toilet is one of the less obvious flood risks, and the maker gives a specific use for FloodSax here: just one FloodSax popped down the toilet prevents floodwater sending water back up into homes from sewers¹. The bag expands to block the pan.

Official guidance covers the same problem in other ways. Surrey County Council advises considering non-return valves in sewage pipes to prevent sewage backing up into the house¹¹. Derbyshire County Council lists special valves on drains to stop water entering through the sewerage system among flood resilience products⁸. A non-return valve is a permanent plumbing measure; a FloodSax is a temporary one you can deploy when a warning arrives.

If a toilet is unusable because of a blockage, Public Health Wales advises considering the use of chemical toilets ("portaloos")¹². For a household plan, decide in advance which toilets you would block and keep at least one dry FloodSax within reach of each. The Home Emergencies: Fire, Carbon Monoxide, Gas Leaks and Burst Pipes guide covers other indoor water problems, including burst pipes.

Soaking up leaks indoors with a dry FloodSax

FloodSax are not only for outdoor floodwater. The maker says they can be used inside to soak up leaks and spills in hard to reach places such as beneath faulty boilers, radiators and pipes¹. A dry bag placed under a drip expands as it takes on water and holds it rather than letting it spread.

This is a useful second role for a household store. A small leak under a boiler or a radiator, caught early, is a job for a dry FloodSax while you arrange a repair. The maker's design means the bag moulds to the space it is put in¹. Keep a couple of dry bags in the cupboard with the stopcock and the boiler, not only in the flood box.

For a leaky toilet, Wessex Water's advice is that it can be fixed relatively easily by someone who is confident with DIY, and if not, the water company recommends contacting a qualified plumber¹³. A FloodSax under a leak buys time; it does not replace the repair.

Storing FloodSax: at least 5 years in good conditions

The maker states that FloodSax have a shelf life of at least 5 years in good conditions¹⁴. Store them dry, flat and out of the way of damp, and check the box each year when you review your household emergency kit. The Emergency Kit: What a UK Household Should Keep Ready guide sets out how a flood store fits alongside water, food and lighting.

For comparison, official guidance says plastic sandbags should last between 2 and 5 years if stored out of sun and rain³. FloodSax store flat, which makes them easier to keep in a cupboard or under a bed than a pile of sandbags. A box of 20 measures 54cms by 50cms by 18cms and weighs 21lbs (9.5kilos)¹, so it fits on a shelf or in a hall cupboard.

Single use after a flood, and how to dispose of them safely

FloodSax are single use once activated. After a flood, the maker gives three disposal routes, and the right one depends on what the bag has been in contact with.

• General waste with salt: cut across the bag diagonally from corner to corner with a knife, pour table salt on the white inners to break down the polymer, then throw it into general waste for landfill¹.
• Separate the parts: slice it open, drop the gelling polymer inners into the household rubbish bin and incinerate the outer cover, which has nylon stitching and is made from a nylon polymer material¹.
• Specialist disposal: a UK specialist disposal company squeezes the water out with powerful equipment and bales the outer covers before incinerating them; call 01484 641009 for more information¹.

The maker's safety instruction is to always wear gloves to reduce the risk of contamination left by the floodwater¹. That matches official advice: Oxford City Council says to discard floodwater-exposed sandbags as they may be contaminated⁹, and government recovery guidance says not to place used sandbags or their components in household waste, not to allow children or pets to come into contact with the sand, and to take contaminated sandbags to the local household waste recycling centre and inform staff¹⁵.

For local arrangements, contact Environmental Health in your local council for information about cleaning up and disposing of waste¹⁶. When cleaning up after a flood, wear gloves and a disposable plastic apron when using cleaning products and follow the manufacturer's instructions correctly¹⁷. Drying out can take weeks or even months, and if it is done too quickly it can cause structural damage and long term problems¹⁸.

Where to buy FloodSax and who makes them

FloodSax are made by Environmental Defence Systems Ltd, based in Huddersfield, West Yorkshire¹⁹. The maker says almost 3 million FloodSax have now sold worldwide¹. They are sold in boxes of 20, in 4 bags of 5, and in carrier bags of 5¹.

For a household, the box of 20 is the natural unit for a flood plan: it gives you four packs of five, enough for a doorway barrier plus a toilet block, with spares. A pack of 5 will soak up to 100 litres of water¹. Buy from a supplier you trust and check the box is intact and dry when it arrives.

Westminster City Council points residents to the National Flood Forum's Blue Pages Directory to find flood protection products and service providers⁶. That directory is a way to compare temporary barriers and other flood products before you decide what suits your home.

Getting warnings and help before and during a flood

A flood store only helps if you know when to use it. In England, the Environment Agency's Floodline is 0345 988 1188, a 24-hour service²⁰. When you call Floodline, enter your quick dial code to hear flood messages for your area directly²¹. You can find out your quick dial code or codes online or by calling Floodline on 0345 988 1188¹⁹. The London Fire Brigade advises calling Floodline on 0345 988 1188 to report flooding in your area, or if your home is flooded²².

In Scotland, the Scottish Environment Protection Agency runs Floodline and publishes quick dial codes for local flood information¹⁹. In Wales, Natural Resources Wales advises checking if your area is at risk of flooding¹⁰.

The Staying Informed and in Touch in an Emergency: A Household Guide covers warnings, radio and phone alerts in more detail. The Extra Help in an Emergency: Older, Disabled and Medically Dependent Households guide explains how to register for extra support if you or someone you care for would need help during a flood.