Bread that's sold at supermarkets comes in two types of packaging: plastic bags (usually with colored tags) and open paper sleeves. Storing loaves in plastic makes sense, since the material is good at blocking air, preventing bread from getting stale or moldy within days of leaving the store. The advantages of the paper bags used for fresh ciabattas and baguettes are less obvious, but according to Southern Living, grocery store bakeries favor them for a good reason.
Unlike name-brand breads baked with sugar and preservatives, fresh bread shouldn't sit on your kitchen counter for days. Most bread baked in-house by your grocery store (or local bakery) is meant to be eaten a day or two after it comes out of the oven. With this in mind, stores choose packaging that best preserves flavor and texture in the short-term.
Paper bags are preferred for fresh loaves specifically because they let in more air than plastic. The porous material keeps the crust dry and crispy, which is what customers want from fresh-baked bread. Plastic blocks air from getting in, but it also prevents moisture from leaking out. So while a sealed plastic bag would stretch a loaf's lifespan, the crusty exterior would quickly become soft in the moist environment.
You can push off your fresh bread's expiration date by storing it in plastic wrap or a resealable plastic bag as soon as you get home—just keep in mind that it won't taste as good as it does straight from the paper bag on the day you bought it. If you're serious about your bread consumption, it may be worth it to make a bakery run multiple times a week, or even consider baking your own. Here are some tips for baking better bread at home.
[h/t Southern Living]