Reusable bags: how "green" are yours?

When the plastic bag ban kicked in on 1 July, most of us were already packing our groceries in reusable bags. The ban cut one source of plastic pollution – the estimated 750 million single-use bags handed out each year, many of which wound up in our waterways.

So how do the replacements measure up environmentally? That depends on your choice of reusable bags and how often you replace them.

Offsetting environmental impacts

Reusable bags chew up more resources and produce more pollution than single-use plastic bags in manufacturing and transportation. On the flip side, they’re designed to be reused many times. After a certain number of uses, this balance tips in favour of reusable bags, although it may take longer than you’d think.

To determine this tipping point, Danish Ministry of Environment and Food researchers calculated different bags’ environmental impacts compared with single-use plastic versions. Published in 2018, the report examined 13 reusable bag materials and estimated the number of uses:

• Needed to offset climate change impacts: the point at which greenhouse gases from making a reusable bag were less than those from producing a single-use plastic bag.
• Needed to offset the full environmental impacts: the point at which making a reusable bag had fewer negative environmental effects (from water use and ozone depletion to the release of toxins and greenhouse gases) than producing a single-use plastic bag.

How long to make an impact

Here’s how many times you’d need to pack your groceries into five common types of reusable bag to justify making the switch from single-use plastic:

Cotton

Example: Life Education bag ($3 from The Warehouse)
Climate change impact: 53 uses (once a week for 13 months)
Full environmental impact: 7101 uses (once a week for 137 years)
Disposal options: Landfill, re-purposing (as rags) or try composting (natural fibres are biodegradable but may be unsuitable for small compost bins.)

Jute (plastic lined)

Example: Trelise Cooper The Eco Bag ($7.99 from New World); Zinc bag ($6 from Countdown)
Climate change impact: 24 uses (once a week for six months)
Full environmental impact: 871 uses (once a week for 17 years)
Disposal options: Landfill or re-purposing.

Non-woven polypropylene

Example: Bag for Good ($1 from Countdown); New World Bag (99¢ from New World)
Climate change impact: 7 uses
Full environmental impact: 53 uses (once a week for 13 months)
Disposal options: Landfill or Bag for Good returned to Countdown for recycling in Auckland.

Paper

Example: Brown paper bag (20¢ from Countdown)
Climate change impact: Once
Full environmental impact: 44 uses (once a week for 10 months)
Disposal options: Kerbside recycling or if contaminated with food, compost or landfill.

Polyester

Example: Warehouse Stationery bag ($1 from Warehouse Stationery)
Climate change impact: 3 uses
Full environmental impact: 36 uses (once a week for nine months)
Disposal options: Landfill or repurposing.

GUIDE Reusable bag availability and cost based on store surveys in July 2019. NUMBER OF USES based on Danish waste system as no comparable research conducted in New Zealand. Paper bags were used as bin liners, not recycled as the research deemed this had a lower environmental impact. Plastic reusable bags were recycled (currently only available at Countdown for Bag for Good). The study did not assess some types of reusable bag available in New Zealand (such as polyester bags made from recycled plastic bottles). DISPOSAL OPTIONS based on New Zealand supplier information and local recycling and rubbish systems.

Hygiene tips

Our food safety advice for reusable bags:

• Have a bag dedicated for raw meat, such as a plastic-lined chiller bag. Let your checkout operator know about it (or pack it yourself). Don’t add any other foods or products. Wash or wipe this bag with hot soapy water and rinse after every use
• Clean your bags regularly. Wipe plastic and jute bags with hot water and dishwashing liquid. Fabric bags can be added to a load of washing or cleaned by hand. As you unpack groceries, check the bags for dirt, stains or spilled liquids – if you see any, give them a wash.
• Store all your bags in a cool, dry place. Don’t use them for anything else (for example, carrying gym or children’s sports gear).

Make your own bag

You don't need to buy a reusable bag – you can make your own from an old t-shirt.