It’s not as though you need us to tell you this is a travel mug or to explain how it works. (Fill with coffee, lift to your lips, sip and – the key – reuse.) But maybe, if you still get your daily cup of coffee in a disposable cup, you do need us to give you a gentle prod. Happy to be of service.

Step 1: Buy a travel mug (Yordprom Coffee in Portland sells them for $12.95).

Step 2: Don’t forget it at home. It won’t do you (or the Earth) any good there.

How many folks in Portland already carry commuter mugs? I took a small and unscientific poll. At Yordprom Coffee Co., “less than 5 percent. I can count on one hand how many people come with one,” owner Tom Yordprom said. At Coffee by Design, “it’s quite common, especially with our regulars,” India Street store manager Krista Lucht said. How common is quite common? “At least one out of 10, probably more,” she replied. Bard Coffee barista Tony Paolino likewise estimated 10 percent.

Travel mugs save on trash and CO2 emissions, according to “If you buy just one cup of coffee or tea in a disposable cup every day, you’ll end up creating about 23 pounds of waste in one year,” the organization says on its website. Commuter mugs save you money, too: 5 cents per cup at Yordprom, 25 cents per cup at Coffee by Design, 50 cents (!) at Bard. Do the math: If you buy one cup of coffee a day from Bard, five days a week, 52 weeks a year, that’s $130 savings per year.

Just who carries his own mug, according to my poll? Regulars (“I think a lot of people know they are going to be in here every day or multiple times a day, and I like to think they became aware of the impact that might have on the environment and decided to just invest in their own mug,” Lucht said.) Middle-aged people (and some in their 30s). Who most definitely does not carry her own mug? 20-somethings, I’m talking to you. Nobody has observed any gender gap.

What’s stopping customers from using commuter mugs? Paolino hazarded a guess: “It speaks to the whole American way. (The disposable cup) is easy. You don’t have to think about it. Some people might find (a travel mug) cumbersome. It’s one more thing to carry. Or one more thing to remember.”

And who should be using a commuter mug? Sorry to sound like your mom here, but look in the mirror. Many things in life are hard. Remembering to carry a travel mug from your car or office to the coffee shop is not one of them.