Handwash would solve the prob. I only go to carwash when im really really lazy. There are soft top care kits selling from bmw dealer. It smells nice but I dont know does it really work.
2009 BMW 650i Cabrio (daily drive)
2011 Audi A4 (groceries, bully, road trip, winter beater, family car)
BMW CCA ID: 473647