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 N7 armour from Mass Effect, Steampunk Valkyrie, Morrigan from Dragon Age, Tiefling Sorcerer from DnD, various random Halloween costumes, Thor Goddess of Thunder
Current/Future costumes: Lady Joker, Polaris from Marvel
Dreamy-dream costumes: Aloy from Horizon: Zero Dawn, Lara Croft from Tomb Raider, Daenarys Targaryen, Lady Groot, Troll/Orc from World of Warcraft