The only information I have regarding durable, intended-for-reuse grocery bags is for canvas, and the carbon break-even point is somewhere ~150 uses compared to

The only information I have regarding durable, intended-for-reuse grocery bags is for canvas, and the carbon break-even point is somewhere ~150 uses compared to getting one-off bags every time. I would guess that heavy-duty plastic would fare significantly better, because cotton in general is an awful crop from an energy input standpoint, but I can't give you a more precise answer than that, I'm afraid.