The Incredibles' super suits are one-piece, so how do they put them on? Do they have to stick their bodies feet-first through the neck hole? Is there a hidden zipper somewhere?
It seems clear that Edna Mode designs suits for each person individually and caters for individual requirements. However, there is no confirmation that any suit is actually only one-piece...but the available evidence is that they are.
When held up they appear as one solid item of clothing.
However, most notable is the suit for Elastigirl
Your suit can stretch as far as you can, without injuring yourself, and still retain its shape. Virtually indestructible...yet it breathes like Egyptian cotton
So, it seems likely that each suit will stretch as much as is needed to put it on and then shrink back to be form fitting as we see.
We know that Bob's old suit was one-piece but stretched up considerably when he wore it so we must assume the new suit is the same.
Note the size when he holds it in his hand:
I am answering this based on The Incredibles.
They wear it just like every other Superhero. It is just fabric but an advanced type.
Mr.Incredible has it covered under his dress. See ending scene of The Incredibles.
Violet's suit is invisible when it comes to contact with her body. So, we can assume that she becomes invisible and changes her dress.
Helen changes her suit like changing dress. It is shown in The Incredibles where she goes to a changing room to change her suit.
They put the masks when there is a need to fight by taking them out of pockets.