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I keep a lot of my stuff organized in normal disposable plastic bags I have left after shopping at various markets. And it works fine, except after a couple years I often find a bag in shreds, simply falling apart. Biodegradable - reaching their end of life, making a mess in my stuff and not serving their purposes. I'd be better off disposing of them or not getting them in the first place. Sometimes they are labeled, but sometimes there is nothing to signify whether they can last years or will fall apart.

Is there a reliable way to distinguish these from non-degradable plastic bags before they start falling apart?

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Most non-biodegradable plastic bags are made of Polyethylene (PE) and often have a marking or logo like this:

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There may also be a marking that say 'PE-HD', 'LDPE' or 'PE-LD'

Bags that are biodegradable usually have a logo on it containing the words 'biodegradable' and/or 'compostable', e.g. something like this:

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If there is no logo or description it's most likely PE, but I don't think you can know for sure unless you get the bag tested in a lab.

BTW, all types of plastic will degrade very slowly under normal circumstances. I don't think biodegradable plastics degrade much faster than non-biodegradable plastics. Most biodegradable plastic bags are made from Polythene film or corn-based materials like Polyactic Acid (PLA). For biodegradable plastics to degrade (in a reasonable timeframe) they need to be heated to very high temperatures for several days.

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Does this answer apply world-wide, or are those logos particular for certain parts of the world? –  gerrit Feb 6 at 9:42
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AFAIK there is no logo that is used world-wide, but in Europe I most often see the first 2 biodegradable logos I've posted. I think the used logo often depends on the (imagination of) bag's manufacturer. –  THelper Feb 6 at 9:49
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I remember several years ago going to a fast food chain and getting my take out in a biodegradable bag. The employees were very enthusiastic about explaining that the bags would break down on their own within a year. There was never an answer when I pointed out that I had several of the biodegradable bags in a drawer in my desk for over a year, and none looked any worse for the wear. The chain has since started using paper... It's always good to be realistic about the biodegradability of these bags! –  michelle Feb 6 at 15:21
    
Compostable plastics degrade quickly, for example, within 35 days. –  BryanH Apr 9 at 19:02
    
@BryanH Only if you put them on a compost heap that has generated a lot of heat or if it is 'home compostable' plastics (see also this post and answer). In all other cases compostable plastics degrade very slowly. –  THelper Apr 10 at 7:06

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