When reusable shopping bags first started becoming popular they were typically canvas bags made of fibers like cotton and hemp. Thanks to its heavy use of insecticides (using 16% of the world's insecticides for 2.5% of the world's cultivated land) cotton is considered the world's dirtiest crop. The environmental impact of cotton production (pesticides, pollution, and the significant amount of water used) is directly correlated to its weight. So when choosing a canvas bag opt for lighter bags, preferably made of organic cotton or hemp.
Polyester is thin and extremely durable. The production of an average-size polyester shopping bag creates as much greenhouse emissions as it would take to produce seven disposable plastic shopping bags.
More often these days you will see bags made of polypropylene. These are those soft, plastic-y looking bags shaped like brown paper grocery bags that most major chain stores offer. In terms of greenhouse emissions, the manufacturing of one polypropylene bag equals 11 disposable plastic bags.
All three reusable bag options are greener than the disposable paper and plastic bags available in stores. Polyester and polypropylene bags are pretty comparable. Both have a moderate edge over canvas. You can feel good about using any type of reusable type. Just remember:
- Reusable bags need to be cleaned. You don't want to be carrying bacteria along with your groceries. You should always choose bags that can withstand a cycle in the washing machine. If you retire a bag once it gets soiled, you're not really being all that green.
- Look for lightweight, but sturdy. Again, if the bag doesn't last very long because it starts falling apart then it can't be very green.
- You have to actually use the bags for them to be green. A reusable bag needs to be used 171 times to negate the environmental impact of one plastic bag. Keep a stash of bags in your car so they're always readily available. And remember, they can be used for every type of shopping not just groceries.