I'd say glue then paint. Watch Evil Ted on YouTube, he has excellent advice on making and detailing foam armour.
Make good art. ~Neil Gaiman
Past costumes:Commander Shepard, Steampunk Valkyrie, Tiefling Sorcerer, Morrigan of Dragon Age, Thor Goddess of Thunder, Daenerys Targaryen
Future costumes: Aloy, Maleficent, Ciri, Steampunk gown
part of Pixelated Cosplay group on Facebook, @cathartic_creation on Instagram