In the first Ant-Man, Hank Pym explained that the special suit and helmet were required to contain the Pym particles in order to vary the person's size. But in Ant-Man and the Wasp, people change the size of cars and buildings without the suit. How is this possible? There is also a scene where Scott becomes small/big without helmet. Did I miss an explanation from movie?
In the first movie, Darren Cross shrinks a sheep which is in a special protective container, which acted as big suit. We can assume that Hank specially prepared the building and cars to work in a similar fashion.