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.