Including organic matter (fibers, charcoal) with the clay makes terra cotta a better insulant.    From Wordnik.com.  [7. Building Instructions] Reference

Terra cotta is a much better insulant than metal, so less heat is lost from a terra cotta stove.    From Wordnik.com.  [7. Building Instructions] Reference

But tinted windows not only saves on your interior but acts as an insulant on the glass, which obviously helps when you're running the air conditioner.    From Wordnik.com.  [CNN Transcript Oct 1, 2008] Reference

It performs both as an insulant and as a thermal-mass and it locks up carbon as it grows.    From Wordnik.com.  [Blogposts | guardian.co.uk] Reference

This air, which is still the most effective insulant known today, limits variations in temperature between the exterior and the interior of the car.    From Wordnik.com.  [Jalopnik] Reference

A mockbelief insulant, ending none meer hyber irish.    From Wordnik.com.  [Finnegans Wake] Reference