Unlined waistcoat/vest? · Real Men Real Style Community

Unlined waistcoat/vest?

In the course of developing my first bespoke fresco suit, one of the questions I'm having is about the lining for the waistcoat.

One of my main goals is for the suit to be as lightweight and breathable as possible. So I'd like to have a vest that is also light, and can be worn standalone. I'm thinking about unlined, as that's typically a road you go with jackets. But I'm not sure how it would work with a vest.

Here is my question. Which vest would be more breathable: