Roast chicken skin usually stays soft because of leftover surface moisture; drying the skin thoroughly before cooking, rubbing it with a thin layer of oil and salt, and cranking the oven up for the last few minutes will crisp it up noticeably.
Why won't the skin crisp up?
Chicken skin crisps as its moisture evaporates and the collagen beneath the fat browns and firms up; if there is too much surface moisture, some of the oven's heat goes toward evaporating that water first, leaving the skin soft and rubbery before it ever gets the chance to brown and harden. Putting a chicken straight into the oven fresh out of the fridge, its surface still damp, is a common cause of this.
A low oven temperature has a similar effect — if the skin never reaches a high enough heat to brown, it can stay soft even once the meat inside is fully cooked. Liquid and fat pooling beneath the chicken on the tray also keeps the underside of the skin damp, making it harder to crisp.
What should you do before cooking?
Before it goes into the oven, the chicken should be patted thoroughly dry with paper towels, and ideally left uncovered in the fridge for a few hours so some of the surface moisture evaporates naturally. Rubbing a thin layer of olive oil or melted butter over the skin along with salt adds flavor while also helping heat reach the skin more effectively.
Roasting the chicken on a wire rack, away from any liquid pooling beneath it, keeps steam from rising back up into the skin, making crisping much easier — chicken cooked directly on the tray's surface tends to trap that steam and delay crisping.
How do you crisp up chicken that has already cooked?
If the chicken is cooked through but the skin is still soft, switching the oven to broil for the last few minutes with the chicken near the top rack is usually enough — just watch it closely and pull it before the skin burns. For smaller pieces, a few minutes skin-side down in a hot pan gives a similar result.
A short extra run in an air fryer also works well, especially for chicken that was already cooked and then chilled in the fridge; the dry, circulating hot air quickly drives off any remaining surface moisture and brings the crispness back.
Does baking powder or a brine actually help?
Dusting a little baking powder over the skin changes its surface pH and speeds up browning and crisping, which is why plenty of experienced cooks reach for it; this is usually rubbed on along with salt at least a few hours ahead, ideally the night before. Brining, on the other hand, is aimed at keeping the meat moist rather than crisping the skin, so it does not solve the crispness problem on its own.
Leaving the chicken uncovered in the fridge after that rub deepens the salt's effect and lets most of the surface moisture evaporate before it ever reaches the oven; combining those two steps gives far more reliable crisping than counting on high oven heat alone.