Various studies have shown that the conventional lightweight supermarket plastic carrier bag, certainly reusable although it is classed as disposable, comes out to be the most environment friendly, as long as it is disposed off properly without causing litter or making its way to the marine environment. Cotton bags turn out to be the least environment friendly primarily due to ozone depletion during cotton production.
The Danish Environmental Protection Agency commissioned a life cycle assessment of grocery carrier bags available in Danish supermarkets with the aim to identify the carrier bag with the best environmental performance over a range of environmental impacts.
The table below provides the results as number of reuses needed for a type of bag to provide the same environmental performance of a lightweight supermarket plastic bag. If the reference - lightweight plastic bag - can be reused more than listed, then the number of reuses for the other bags should also be increased proportionally.
| Bag type | Example | Reuses necessary to have same environmental impact as a lightweight supermarket plastic carrier bag | | |
|---|
| | | | |
| Lightweight plastic bag with rigid handle |  | 0 | | |
| Lightweight plastic bag |  | 1 | | |
| Recycled plastic bag |  | 2 | | |
| Polyester bag |  | 35 | | |
| Bio-based plastic bag |  | 42 | | |
| Paper (bleached or unbleached) bag |  | 43 | | |
| Woven polypropylene (PP) bag |  | 45 | | |
| Non-woven polypropylene (PP) bag |  | 52 | | |
| Recycled polyethylene terephthalate (PET) bag |  | 84 | | |
| Bag made of multiple materials (plastic, cotton, jute, etc.) |  | 870 | | |
| Conventional cotton bag |  | 7,100 | | |
| Organic cotton bag |  | 20,000 | | |
| | | | |
A life cycle assessment of supermarket carrier bags conducted by the UK Government had similar results requiring many reuses of paper, more durable PP & cotton bags to have equivalence to global warming potential of a conventional, lightweight carrier bag.
The results of yet another life cycle assessment by the Heartland Institute show that conventional plastic bags use less energy & water during manufacturing, emit fewer global warming gases, less acid rain emissions, and less solid wastes - over both compostable plastic bags and paper bags.
These reports do not consider the effects of littering, including marine litter.
Whatever type of bag is used, the key to reducing the impacts is to reuse it as many times as possible, even for those classed as 'disposable', and where reuse for shopping is not practical, other reuse, e.g. as bin liners, is beneficial. Recycling or composting generally produce only a small reduction in global warming potential.
Bibliography
Bisinella V and others, “Life Cycle Assessment of Grocery Carrier Bags” (The Danish Environmental Protection Agency, 2018)
Chaffee C and Yaros BR, “Life Cycle Assessment for Three Types of Grocery Bags - Recyclable Plastic; Compostable, Biodegradable Plastic; and Recycled, Recyclable Paper” (Heartland Institute, June 2014)
“Life Cycle Assessment of Supermarket Carrierbags: A Review of the Bags Available in 2006” (GOV.UK, July 2011)
“Would Using Biodegradable Plastics Solve the World’s Plastic Problems?” (OneSharedEarth, April 2018)
