The most sustainable object is the one that never gets made.

For a drill, a tent or a bike, the heavy part is not the use. It is the making: extracting the materials, processing them, assembly, packaging, shipping. That cost is paid once, when the object comes into existence, and it stays paid whatever happens next.

If ten people share one drill instead of buying ten, nine of those costs are never incurred. That is a subtraction, not an offset, and it is why renting weighs more than most of the individual gestures we tell ourselves about.

There is a simple way to decide without doing sums. Count the days you will genuinely use something across its whole life. Under ten, renting almost always wins: on money, on the space it would take at home, and on the supply chain that does not have to make another one.

Above ten days the maths flips and buying makes sense again, second hand if you can. We have no interest in arguing otherwise: an object bought and used for years is a good outcome.

We do not publish a figure for kilos of CO2 saved, because doing it seriously needs data for every category of object and a method that survives outside scrutiny. Until we have both, a round number would be decoration.

What we can say is what matters in a rental: the type of object, how many times it circulates, and how far it travels to do so. When we have numbers that hold up, they will appear here.