Materials are awarded on a sliding scale. 3 materials for your first play of a mission, 2 materials for the second, and 1 material for the third. You will receive no materials for any plays of that mission beyond that, but you'll continue to collect supplies.
Materials are awarded for story missions only (Seasons 1 - 6). Materials are not given in the other missions types as these take place outside of the main storyline, and are designed to be replayable.