Plastic does not care about conditions. Your skin still does.

Dry air, warm room, same holds all month.

Outside, rock texture and weather change every session. Inside, the texture is constant, the room is heated, and the holds are the same ones you fell off on Tuesday. The top layer of skin polishes smooth on grippy plastic and stops sticking. Then the room warms up, the hands sweat, and chalk turns to paste on a hold two hundred people have touched.

Gym climbers need two things: water in the skin so it grips instead of skating, and less sweat so it stays that way through the session. Volume is the third problem. Three or four sessions a week do not leave much time to grow skin back, so the overnight routine matters more than it does for a weekend crag climber. Everything here was tested in gyms before it ever went outside.