If your aim is to reduce the amount of plastic in the environment, replacing single-use plastic bags with heavy-duty, multi-use ones just may not really add up.

According to a British study published in 2011, (British life-cycle assessment) you’ll need to reuse a heavy-duty bag at least four times to recoup the extra energy needed to make it, according to the comparative energy costs of different bag materials.

Research has found that about 1 per cent of plastic bags used in Australia end up in the environment. This seems a very small amount. However, it is estimated that about 10,000,000 bags are consumed in Australia every day. That amounts to about 100,000 bags.

The problem is, if the heavier-duty bags that stores such as Woolworths, Aldi and Coles are now selling (for $0.15 each) reach the oceans and other habitats, they could cause as much if not more damage than single-use bags currently do. This is because heavy-duty bags can take much longer to break down.

Both the two big supermarkets in Australia claim their heavy-duty bags are made from 80 per cent recycled material, which is a benefit as this would mean that less raw materials are needed in the manufacturing process. There are other benefits in regards to the Life Cycle Assessment of bags using 80% recycled materials such as reductions in transport costs to the environment.

But the problem that Aldi found, who have not provided free single use plastic bags at all since opening in Australia, is that people don’t tend to reuse them. They use them as bin liners, use them to store other items or simply dispose of them and they end up going into landfill often after only one use for groceries.

Take your canvas or cotton bags

The alternative Canvas, although traditionally made from hemp, is now produced from linen or cotton.

The first thing you need to know if climate change or water scarcity are your concern is that you’ll need to use your canvas bags about 100 times before you’re ahead of single-use plastics.

Exact figures are difficult to calculate because there are so many variables such as where the cotton is grown and where the bag was made.

But an analysis by the British Environment Agency estimated that from a climate change perspective, cotton bags need to be used 131 times before they break even with single-use, high-density polyethylene (HDPE) bags.

Cotton is also extremely water intensive.

A hectare of cotton takes almost 8 million litres of water to grow on average, and about 90 per cent of Australia’s cotton comes from the Murray-Darling Basin, where water scarcity has become a major issue.

The good thing is you can use cotton bags hundreds or thousands of times, they’re washable, and biodegradable.

So you can also throw your cotton bag into the compost when it comes to the end of its life.