The answer to this question varies greatly depending on how often you use your items—if your raincoat only gets thrown on to walk the dog once a week, you’re going to have to do it less often than someone spending weeks thru-hiking in the spring—but a good rule of thumb is at least once a season. Then you’re going to want to reapply a waterproofing product (after washing, of course) any time you notice an item “wetting out” again.  “DWR is the best,” Nagode says. “Once that wears out, and washing and drying don’t bring it back, then you need [a waterproofing product]. The older a jacket is, the more maintenance it’s going to require.”  Your items’ DWR coating won’t always break down evenly across an item; for instance, a raincoat is more likely to wet out in areas where it has contact with oils from your skin or other pieces of gear, such as where your backpack straps rub it.