These defectors are held in the window channel by friction and spring tension.
They work very well, and I have had front and rear sets on all of our vehicles for the past 10+ and include a 1997 Passat TDI sedan and a 2010 TDI Sportwagen.
These defectors help alleviate wind buffeting when the windows are down, and allow the windows to be open to vent on hot days without it being apparent to passers by. They also do a great job of deflecting rain.
Now that they are available, I'll order a set for our new TDI SEL.