Unlike the almost entirely CGI Yellowjacket suit worn by Darren Cross (Corey Stoll) in Ant-Man, the Ant-Man suit worn by Scott Lang (Paul Rudd) is a real costume.
Accoring to this article by ScreenRant;
Rudd suited up in the outfit to shoot his scenes with the helicopter and he wanted to show it off but couldn’t find us since we were checking out the third unit, where Ant-Man’s unique macro photography was taking place. So, in between takes when we were back in the first stage, he came in the room, fully suited up. He had to have an assistant unscrew the front of his mask so we could see his face.
So it would appear that although the helmet itself existed as a real part of the costume, it is unable to open up as easily as seen in the film.
However, this article from The Nerdist says;
Seventeen helmets were made over the course of the production. The stunt helmets were more rubbery and flexible whereas the hero helmets (the ones used for close-ups) are more durable and have more delicate parts.
So it is entirely possible that the one shown off by Paul Rudd to ScreenRant was simply one that couldn't open up as it is shown in the film. The Nerdist article also says;
The Ant-Man suit is fully functional in terms of electronics and freedom of movmenet[sic]. Using small circuit boards, the suit can light up and generally makes you look like a badass. Pym Particles are sold separately.
Which helps supports the theory that of the seventeen helmets created for the film, one of them may have been able to open up the way we see in the movie.
However, this is far from conclusive. All we can really take from these articles is if there is a version of the Ant-Man helmet with a working opening faceplate, it hasn't been seen (or at least mentioned) by anyone in any interviews I can find. Personally, I would imagine that the working parts required to have the faceplate open up would be more costly and complicated than simply using CGI to create the effect, but unless someone can find an article with an in-depth look at each of the seventeen helmets created, it is impossible to say for sure.