One of the main reasons people avoid steel bottles is because they are considered heavier than sports (plastic) bottles. But are they really?
THE UNDENIABLE FACTS
Ion8 publish the specifications of their products, so this is pretty easy. Just look at the size chart, you can see which is lighter. It's clear - plastic is lighter. Game over. Steel appears not to be as light as plastic. Take the Slim, for example.
Hardly a surprise!
BUT THINK ABOUT THIS...
Who carries around an empty bottle? What really matters is what they weigh when they are full and being used. And that is much more interesting...
The reality is that the Double wall bottle actually holds a little less - but it will keep that water cold for hours.
So you can decide whether you prefer to carry a bit more water, or whether you prefer to have that water cold (or warm).
The weight, surprisingly, is hardly a factor.