Are paper bags actually better than plastic bags?

It depends entirely on which impact you measure and how many times each bag is used, which is why the question rarely has the clean answer people expect.

By production impact, paper is worse than single-use plastic. A paper bag requires more energy and water to manufacture, generates more greenhouse gas emissions, and is heavier to transport. Several lifecycle assessments put paper's production footprint at several times that of a thin plastic bag.

By end-of-life impact, paper is better. It degrades, is widely recycled, and does not persist in the environment or fragment into microplastics. Plastic's durability is precisely what makes it harmful once discarded.

Reuse is what reconciles these. Because paper's higher production cost is paid once, reusing it several times closes much of the gap. The same logic applies more dramatically to heavier reusable bags: a cotton tote has a far larger production footprint than either and needs to be used many dozens of times before it comes out ahead on emissions, which most people never do.

That is the genuinely useful conclusion. The bag with the lowest impact is almost always the one you already own, whatever it is made of, used until it falls apart. Acquiring new reusable bags repeatedly is worse than reusing a plastic one.

The secondary consideration is local. Where littering and marine pollution are significant problems, plastic's persistence weighs heavily. Where waste is well managed and emissions dominate the concern, the calculation shifts.

Either way, single use is the problem rather than the material.