Best way to test consumer reaction to sustainable packaging changes?

Surveys are fine but honestly conjoint analysis will give you much richer data — it forces trade-offs so you see if sustainability actually drives purchase decisions vs. just getting polite 'yes I care' answers. Pair that with a small in-store or shelf simulation test (even virtual shelf via tools like Wyrd or Shelfgaze) to catch real behavioral reactions. 200-300 respondents is usually enough to get solid directional results for packaging work like this.