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, Morrigan, Tiefling Sorcerer, Morrigan of Dragon Age, Thor Goddess of Thunder
Future costumes: Aloy, Maleficent, Ciri
part of Pixelated Cosplay group on Facebook, cathartic_creation on Instagram