Updated on 04.20.10

After seeing more than a hundred comments and several dozen emails about the rewashing Ziploc sandwich bags article from last weekend, I felt it was appropriate to address the most common follow-up question:

You’ve mentioned yourself in the past that you re-wash Ziploc bags! What gives?

I do, in fact, rewash those large, ultra-durable gallon-sized Ziploc freezer bags. Those bags have a very different cost proposition than the cheap, flimsy sandwich bags. I think it’s only fair to run through the calculations on these bags as well.

As before, let’s get the data.

First of all, according to my own experience, you can wash and re-use a single Ziploc gallon-sized freezer bag an average of nineteen times, for a total of twenty uses. My test, as with the sandwich bags, is seeing whether or not the bag will hold water afterwards.

I also timed how long it took to handle each individual bag to properly clean and dry it. In order to get it clean and also get it appropriately dry, you have to pre-rinse the bag a bit, then carefully spread it across as many dishwasher tines as it will fit around. With some practice, I was able to get this procedure down to about twenty seconds a bag, just the same as a sandwich bag.

How much water and detergent is used to wash a bag? I could fit eight bags on the top rack of our dishwasher. According to my calculations, the cost to run a full load is 15.6 cents worth of detergent and water. This means each bag uses 0.9 cents’ worth of detergent and water to get clean, again, the same as a sandwich bag.

Several people wondered about the details of this calculation. I am able to get eight Ziploc bags on the top rack of the dishwasher. Imagine putting the bags in there in a three-by-three pattern, then taking out the central bag because it would cover up the spout connecting the top and bottom shelves. That gives you eight bags which, on the whole, take up half of the space in a dishwasher load. Since a load would cost 15.6 cents, the eight bags themselves cost 7.8 cents to wash, averaging out to 0.9 cents per wash.

How much do such Ziploc gallon freezer bags cost? You can get 152 Ziploc gallon freezer bags for \$10.98 at my local Sam’s Club. This calculates out to a price of 7.2 cents per bag.

If you can’t already tell, the math in favor of washing bags is much better for gallon freezer bags than it is for sandwich bags. Let’s do the math.

Over twenty uses of a Ziploc freezer bag, you can either buy twenty of them at 7.2 cents a pop (total cost: \$1.45 after figuring in rounding) or you can buy one of them for 7.2 cents, do nineteen washes at 0.9 cents a pop (total cost: 24.3 cents), and invest six minutes and twenty seconds in the washing.

Thus, the savings for rewashing gallon Ziploc freezer bags (assuming the 20 seconds per wash I state above) is \$11.46 per hour of washing effort.

Many people claimed the time investment per bag is less – it might just be that I’m painfully slow at this. If you spend only ten seconds per rewash, then the savings is \$22.93 per hour.

This is much more palatable for my time investment than the dollar and change per hour that you would earn rewashing Ziploc sandwich bags. Add on top of that the environmental factor – putting plastic in the garbage isn’t the best environmental choice – and I’m pretty happy rewashing the gallon freezer Ziploc bags. The sandwich bags? Not so much.

Another note: the best solution for sandwich bags is to minimize their use. Use sturdy, reusable containers instead, like Rubbermaid containers, that are practically invincible. These will easily hold sandwiches and the like. The only time I use Ziploc sandwich bags is when our children leave the house without us and have a brown bag in hand, because if I sent reusable containers with them, the odds aren’t the best that I would ever see the containers again.

1. Aleriel says:

How is “savings per hour” a meaningful metric in this case? What does it mean that I’m saving \$11/hr washing my bags? What is that compared against? I’m pretty sure I don’t spend more than \$11 every hour on freezer bags, so I’m confused.

Wouldn’t calculating how many bags are used per year (roughly) and figuring out how many bags would be saved (i.e. not have to be re-bought) give a clearer picture?

2. KC says:

I think things like re-using bags are done by people who want to save money, but also not put a zillion plastic bags in the landfill. There are many frugal things I do that don’t have as much to do with saving money as they do with reducing all the trash I create. Someone could show me that it actually costs me money to reuse plastic bags and I would continue to do so.

3. sewingirl says:

You wash your bags in the Dishasher?! Good Grief, I can hear my Grandma rolling over somewhere! She was the queen of baggie washing. Summertime saw as many drying baggies on her clothesline as socks. Hand wash in soapy water, swirl thru the clean rinse water. Towel dry the outside, turn inside out and do the same. Stand inside out baggie upside down on cupboard to finish drying, or clip to clothesline. She also clipped them to the bottom of the roller shade over the kitchen window. Unless you use dozens of bags daily, this will do ya!

4. Shannon says:

5. Leah says:

@ #3, sewing girl — my Grandma, too! Except she was too cheap to even buy ziploc baggies — she reused bread bags over and over and over in the same fashion — hand wash, rinse quickly, hang on the line!

6. Sunny says:

What’s the environmental impact of washing ziploc bags versus throwing them out? Water is going to become increasingly scarce and therefore more valuable. We have well water so I’d have to factor the cost of wear and tear on my system; city dwellers have both water and sewer charges to consider.

7. Jillian says:

Agreed on the handwashing. Why waste all that time and space in your dishwasher when a quick swirl in the sink will do?

I actually don’t even bother to wash most of mine. I mainly use them for muffins and other baking and just tip the crumbs out before I reuse them. I store them in the freezer between uses so any potential bugs don’t get a chance to multiply.

8. asrai says:

@sunny
What’s the environmental impact of all that plastic in the landfill? Water is more renewable than plastic which never biodegrades. I try not to use throw-away platic. But if people insist on using plastic, what they do to reduce it’s use is a good thing. Far more than the extra use of water.

9. Pop says:

At some point, you’ve got to calculate the savings per hour on the time you spend calculating savings per hour.

10. MP says:

About the only time I don’t reuse a heavy duty ziplock is when it has contained raw meat – especially chicken. Then I just wouldn’t trust it getting sanitized enough.

11. Jodi says:

Dishwasher?!? I’m with sewingirl #3. That’s a waste of water and money. (And time, if it takes you 20 seconds a bag to put them in)

Just wash them in warm soapy water, rinse, and hang to dry. It’s quick, and the freezer bags can last for years. When they are holey, I punch more holes in them and use them to store things in the root cellar that need some moisture retention (i.e. carrots, beets).

12. JT says:

Ha ha ha…this post made me chuckle. Dishwasher? Really? I wash my baggies in the sink and let them hang around to air dry. I guess I never put that much thought into it. I just do it cause, well, I dunno, why throw something away if its still good?

13. Diane says:

I wash them mainly to reduce solid waste. It saves some money, but it also reduces trash. I just wash/rinse briefly in the sink and hang to dry. Unless they’ve had raw meat in which case they get tossed.

Size of bag doesn’t matter – I wash them all.

14. Diane says:

I wash them mainly to reduce solid waste. It saves some money, but it also reduces trash. I just wash/rinse briefly in the sink and hang to dry. Unless they’ve had raw meat in which case they get tossed.

Size of bag doesn’t matter – I wash them all.

15. deRuiter says:

#3 Sewingirl, I LOVE your Granny! Her technique for washing out the bags is my technique also. We reuse “store” bags which are free. Bread wrappers are my favorite, they’re sturdy, and I can’t bear to throw them away after the bread is gone. Bread wrappers are pressed into service as storage bags, after being turned inside out briefly to get rid of crumbs. After the first reuse, the bags are swished through the dish water and rinse water, and then air dried. The more items which can be reused, the emptier the landfill, the better and cleaner the environment, the more money in your pocket, the less money sent overseas to ruin the balance of trade. It’s win / win / win!

16. michael bash says:

Since you’re working to learn how to write, let me suggest “indestructible” for “invincible”. We’re talking economy not warfare.

17. I am all about re using those big ones–unless they have had raw food in them.

I thought you guys were talking about the little ones.

That to me, is going a little too far!

Its all good with the big ones though–you can use those suckers forever!

18. Vtcouponqueen says:

It kills me to use them as it is so washing them out eases my mind and saves me money. Here is a great trick for drying them quickly. Hang them upside down open from your fridge with a magnet to hold the in place. In less than an hour they will be completely dry. Whenever I need a bag I look their first and can usually find one.

19. GayleRN says:

Ummm, why not use reusable containers here too? They come in all sizes and shapes.
Maybe I am not so enamored of ziploc bags because I grew up before they were invented.

20. Jackie says:

I wash ziplock bags also and like #3 & #5 said, I handwash them with the dishes, I dry the outside of the bag and sit them somewhere to dry. I reuse bread bags too. I take them out to the porch and shake out all the crumbs, fold and put away until needed. Botton line is that it seems crazy to through all these away and then go to the store and buy new ones. They all end up in the landfill or recycled. Every \$ saved is something to think about.

21. Anitra says:

We hardly use sandwich baggies – like you, Trent, they only tend to get used in cases where a hard container might not make it back home.

For convenience, you can’t beat the cheap plastic containers made by Glad, Ziploc, etc. If we lose them or break them, it’s not a big deal, and they can be recycled if they get broken. And they keep sandwiches from getting crushed!

22. I do it so I don’t have so much trash. I do handwash them like #3,8 and 20.
I’m currently trying to see how much I can cut down on my trash consumption- out of all of the things I’ve cut back on this is the hardest.

23. Trent says:

“At some point, you’ve got to calculate the savings per hour on the time you spend calculating savings per hour.”

Well, part of the content for The Simple Dollar is calculating such things, and that’s part of my income. I calculate such things so others don’t have to.

24. Ben says:

My technique: Put small amount of water and soap in each, close, then use a rubbing your hands together motion on either side to get some scrubbing going inside the bag. Finally, rinse.

I hang them on a shoe rack.

25. Kevin says:

@KC:

“things like re-using bags are done by people who want to … not put a zillion plastic bags in the landfill”

@asrai:

“What’s the environmental impact of all that plastic in the landfill?”

(This is the part where you say, “Because they take thousands of years to break down!” I’ll save you the typing and assume that’s your response).

So what?

Honestly – so what? Who cares if they end up in landfills? What’s the problem? They’re not toxic, they’re not going to leach into the water table. Once they’re buried under 50 feet of dirt, who cares? Is it worth all this effort just to prevent a few baggies from ending up covered in dirt, never to be seen again?

I don’t get this irrational hate-on for landfills. Once it’s covered in dirt, who really cares? I mean, think about it. Right now, wherever you are, what’s 50 feet underneath you? Chances are, you’re at home right now. So if you could dig down 50 feet, all you’d find is rock. How would your life change if it was a plastic baggie instead of dirt? It wouldn’t! Not in the least! So what’s really the problem with landfills? Why is burying Ziploc baggies really a problem? So it takes 50,000 years to decompose, so what? The rock 50 feet beneath you right now has been there for several millennia – is it really affecting your life? Obviously not.

My city has both recycling and composting programs. As such, our garbage output is actually pretty tiny. Our garbage consists almost entirely of non-recyclable plastics (the cling wrap and styrofoam that fresh meats come packaged in, bread bags, milk bags, that sort of stuff). None of those things pose a hazard to the water table, so what’s the problem with just burying it?

26. Cambo says:

Boring as batshit. Who cares if you save a cent by washing. This is what makes frugal look boring. Don’t wash plastic which is a waste product, throw it out for gods sake or let me slash my wrists.

27. Jane says:

I have to admit, I rarely buy sandwich zip locks and when I do the box lasts for over a year. I mostly use them for holding small items. I do not use them for sandwiches. I rarely use them for food unless it is for snacks for the car (which are usually dry like nuts and dried fruit..) so I can reuse them when I am done.
But the idea of using the dish washer to wash ANY bags? I would think the water would get to hot for them in the first place. Then I turn them inside out and let them air dry. It takes but a few minutes to dry..
I wash them out as Ben #24 does. I use about a drop or two of dish detergent..original Dawn. If you use more it takes too much water to get the soap out! Then I turn them inside out to really rinse the inside surface and let them air dry.

28. DivaJean says:

I’m with others as above.

Baggies are not really worth it to me. We buy a box of the smaller freezer size and do wash them out for re-use purposes, but I’d rather just re-use other bags that find their way into our lives– or use some type of plastic ware for packing lunches, leftovers, etc.

Case in point- so much of what we buy comes in bags. How hard is it to empty out the end of the cereal (known as cereal dust in our home) into the garbage, then give that bag a quick rinse out and let it dry on the dish drainer? Not at all. There are MANY similar bags we encounter and toss all the time. Why is so resourceful to wash and reuse ziplocs but no mention of all these other bags? Heck, even if you buy from the bulk bins, you are taking a plastic bag with your purchase. And bread bags- those just get shook out and used for my sandwiches when I pack my lunch. I don’t worry if it gets home or not– it already doubled its usefulness.

29. Marle says:

The average dishwasher uses less water than handwashing. A dishwasher will take about 3 gallons of water to wash the entire load, while your sink faucet uses about 2 gallons *every minute* it’s running. Can you wash a full load of dishes (and baggies) while only running water for a minute and a half?

Also, #25 Kevin, while it wouldn’t matter if there was one plastic bag under my house, it’s never just one. Landfills are giant mountains of trash. My city tried to build a shopping center on top of one. But it was too unstable for that, and Walmart closed after the land resettled and broke the sewer pipes to the bathrooms and made a large crack in the cement behind the store. So I am glad there is not a landfill under my house. Trash all has to go somewhere, and if none of us care how much trash we make, then we’re eventually going to run out of room for all of it.

In the end though, I think that reusable containers would be better than reusing bags. They’d last longer, and it would be easier to wash and reuse them without breaking them, and also I’d worry that since the bags weren’t designed to be dishwashed that the heat and stress of reuse would cause it to break down, and plastic breaking down in your food IS toxic. So, reusable containers for me.

30. Jon says:

My sister says she saves \$30/month washing dishes by hand (she has 4 kids) on electricity. Probably not worth the time investment but if you enjoy the time like I do to listen to podcasts it definitely becomes worth the time (I work from home so don’t have the time in the car). Or if you do dishes w/ your kids it could be worth the time too.

31. Sonya says:

I tell ya, the biggest trouble I have w/ reusable containers is my kid’s teacher see no need to keep them around- so when the 1st grader leaves her lunch bag at school (this is after the box has already been left…) the teacher just tosses bags. So I rarely use even gladware in paper or re-purposed bread or kids meal bags cause it’ll go right in the trash w/ the teacher! Now if she’d clear out the forgotten lunch boxes as often & remind the kids to take them home…. we’d be fine!

32. Claire says:

I tried washing some of those “green” produce bags in the dishwasher and they ended up clogging the dishwasher drain. So be careful with that.

33. Sunny says:

@asrai – my point was that Trent’s calculation didn’t include the cost of water and waste water. I’m a financial analyst and it drives me crazy when people come up with cost savings without looking at the big picture.

I get that we shouldn’t fill the world with plastic, I’ve been recycling/composting since the 70’s.

Happy Earth Day!