Last winter I used Megs #16 over Megs #20 on 1 car and #16 over NXT on another. Both made it 10 weeks before beading stopped, slickness was gone and failed Meguiars "squeak test". This winter I will try Collinite's 476S and see how long that holds up. As far as washing, I use QEW, works great for me winter and summer.