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An op-ed in the Wall Street Journal argues that many re-usable grocery bags are made using more oil than old-fashioned "single-use" plastic grocery bags.

Standard plastic grocery bag

This makes sense, as quite a bit more material is required to make a sufficiently sturdy bag, and many of the lower-quality bags are made of plastic, nylon, or polyester.

Cheap reusable bag

Obviously bags made of canvas, burlap, or something similar are best, but if I'm at the check-out line, don't have a reusable bag, and opt to buy a cheap one from the store, how many times will I have to use it before it's better than just using the single use bags?

Higher quality burlap bag

  • I appreciate this question. But I wonder about the limits of "re-use" and what that idea implies. What can the plastic bag also be reused for? it also speaks to the feasibility (but not offset cost) of paper, which can reused for wrapping, mulching, arts and crafts, and other things besides bagging. – ychirea1 Feb 6 '17 at 18:23
4

Summary: According to this independent study if you look at global warming potential, for a sturdy LDPE bag you need to use it at least 4 times, for an even sturdier non-woven PP bag with inserts it's at least 11 times, and for a cotton bag at least 131 times. These numbers are higher if you reuse your single-use HDPE bags for other purposes


In 2006 the governmental Environment Agency of the UK issued an independent study to find out which type of shopping bags are most environmentally friendly. They compared a conventional light-weight bag made from HDPE with:

  • A paper bag
  • A thick-gauged or heavy-duty LDPE bag
  • An even more durable bag made from non-woven PP, including stiffening inserts
  • A cotton bag

The study concluded that:

  • The paper, LDPE, non-woven PP and cotton bags should be reused at least 3, 4, 11 and 131 times respectively to ensure that they have lower global warming potential than conventional HDPE carrier bags that are not reused. The number of times each would have to be reused when different proportions of conventional (HDPE) carrier bags are reused are shown in the table below.

The amount of primary use required to take reusable bags below the global warming potential of HDPE bags with and without secondary use

The full report is available here: Life cycle assessment of supermarket carrierbags: a review of the bags available in 2006

However there are some caveats:

  • Although the study did investigate other impacts, the table shown only takes global warming potential into account.
  • This particular study is about 6 years old and uses data on bags that were used 10 years ago. New production techniques used today may lead to different results.
  • The result of a life-cycle assessment study done in the UK may not translate to other countries. To investigate this you need to carefully check all the geographical dependent data that was used.
  • Other life-cycle assessment studies have different conclusions, but some of the industry-sponsored studies are known to make assumptions that tend to favor certain types of bags.
  • Any sense on how production techniques may have changed, and which way that would shift results? Assuming the steady march of progress, I wouldn't be surprised if the reuse requirements stayed the same, while the impact of all bag types dropped. – LShaver Oct 8 '17 at 17:31
  • I'm not sure if and how it changed. I suspect the biggest changes have to do with using more recycled plastic and paper. I think recycled cotton is used rarely (at least that's the case where I live), so that would mean that the impact of the plastic and paper bags are relatively lower than now compared to the cotton bag. – THelper Oct 10 '17 at 9:14
  • BUT if you do as I do and make the cotton (or any fabric) bag from old clothes then line 4 looks entirely different. – RedSonja Oct 25 '17 at 12:32
  • According to this article including results from a recent Danish study, if you look beyond GWPs, the necessary re-uses balloon to 10- or 100-fold greater. Rather discouraging. – LShaver Jun 6 '18 at 19:46
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The cheapest reusable bags round here are made of the same plastic as disposable bags. In this case the number of uses required is simply the ratio of the weights. Without getting the scales out I think this is around 10-20 times. They're also bigger so that's not even 10-20 shopping trips unless you only ever buy a little. I know I've had a few hundred uses out of such bags in the past (a design with a season and year, used minimum twice a week for two years) so it's perfectly possible to do quite well.

A major reason for reusable bags (and the reason we now have a charge on disposable bags here) can't be quantified in quite the same way: plastic pollution, especially ending up in the sea. Number of items is an issue as well as total quantity in this case, and fewer bags being used means fewer to cause problems.

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