Quick Answer — Avoiding Plastic Beats Recycling It
The EPA's WARM (Waste Reduction Model) distinguishes between two different climate levers: recycling (diverting waste that would otherwise go to landfill) and source reduction (avoiding the plastic's production in the first place). Source reduction avoids more emissions per ton than recycling, because it eliminates the extraction, manufacturing, and transport emissions of making the item at all — not just the end-of-life disposal impact.
This calculator uses EPA WARM source-reduction factors: avoiding a ton of HDPE plastic (milk jugs, detergent bottles, some grocery bags) avoids about 1.42 metric tons of CO2e, and avoiding a ton of PET plastic (water and soda bottles, most clear food packaging) avoids about 2.17 metric tons of CO2e — both larger than the roughly 1.06 metric tons avoided by recycling a ton of mixed plastic instead of landfilling it.