The way to keep a homemade loaf's crust from going soft is to not seal it in a container or bag before it has fully cooled; if the steam inside a warm loaf cannot escape, it condenses on the crust and softens it into a chewy texture within a short time.
What should you do right out of the oven?
As soon as the loaf comes out, set it on a wire rack so air can circulate underneath; a loaf left directly on a counter or board sweats on the bottom and softens there. Cooling fully usually takes 1-2 hours, and slicing before that point also contributes to premature softening; cutting into a warm loaf right away also leaves the crumb noticeably damper than it should be.
Once cool, the loaf can be left cut-side down on a board or placed in a paper bread bag; paper does not trap all the moisture, so it keeps dust off while letting the crust stay crisp longer than plastic would.
Why does plastic ruin the crust?
A plastic bag stops the loaf's internal moisture from escaping at all; that moisture works its way back into the crust over time and softens it. If plastic is used to keep the crumb from drying out, the crust can be freshened separately in the oven for a few minutes afterward. Even then, letting the loaf cool uncovered for at least half an hour before bagging it reduces how much moisture ends up condensing on the crust.
What if it needs to keep for longer?
Bread that will be kept longer than two days should be frozen; wrapped tightly, whole or sliced, it holds its quality for 2-3 months in the freezer. Thawed at room temperature and then warmed for a few minutes at 180°C, the crust comes back almost as crisp as fresh from the oven.
How do you refresh stale bread?
A loaf with a softened crust can be revived by lightly sprinkling it with water and heating it at 180°C for 8 to 10 minutes; the water turns to steam in the oven heat and crisps the crust again. This works best when done just as the crust starts to soften, before the loaf goes fully stale.
Is a bread box worth using?
A wooden or ceramic bread box protects a loaf from dust while letting some moisture escape, similar to a paper bag; a box with a few small vent holes gives better results than a sealed plastic container for anyone trying to keep the crust crisp. A thin-crusted baguette softens far faster than a thick-crusted country loaf, so baguette-style bread is best eaten the same day, ideally within a few hours of baking. A sharp, serrated bread knife also makes cleaner slices without crushing the crust; a dull knife tends to press the crust into the crumb and can speed up staling.