You can reuse these deodorizers a few times before they lose their deodorizing strength- just place them in the sun for a few hours to rejuvenate and reverse the chemical absorption process by which charcoal neutralizes odors. When I’m traveling, and need to wear my shoes daily, I usually throw a packet away after about five days. With handling every morning and night, the charcoal sometimes begin leaking through the creases of the envelope after 4-5 days- although these tiny manilla coin envelope tends to significantly reduce the escape of charcoal. The envelope has to be very agitated before it begins to show signs of leaking, and the leak is very slow– making it easy to dispose of before it makes a mess. If you’re using these on shoes that are in storage, in drawers, or on luggage, you can keep the packets in place for weeks or months. Replace about every three months- or sooner if the environment is very odorous. Despite what the manufacturers of “reusable” charcoal shoe deodorizers claim, charcoal has a limited capacity for binding and neutralizing odors. Although placing it in the sunlight may improve the charcoal shoe deodorizer's ability to absorb odors – even commercially produced charcoal shoe deodorizers have a limited capacity. For this reason, I prefer to make my own using the sustainable materials in this tutorial.