What's the best way to track consumer sentiment around sustainable packaging?

Honestly, combine both — social listening catches unprompted sentiment (Brandwatch or Sprout Social work well for this), while surveys let you quantify how much it actually influences purchase decisions. A quick conjoint or MaxDiff study can tell you exactly how eco-packaging ranks against price, convenience, etc. The social data often tells you *what* people care about, and the survey tells you *how much* they actually care when buying.