What's a device that minimizes heat transfer?

A device that minimizes heat transfer  is thermos. Technical name is vacuum flask.

Explanation:

Thermos is a bottle in which vacuum separates it from the surrounding. When the bottle is surrounded by the vacuum, there is a significant minimization in conduction.

The only part that having point of contact with the bottle inside is the thing which holds it in respective place. But there will be a small piece of contact, which will make the inner bottle to conduct heat to a small extent.

a and b sometimes have a positive value

b.a device that inputs heat into a cool object