Really depends on how thick it is. If it's too thick it may block out some of the heat. If it's thin I doubt it will make much difference.

I use simple plastic hides or small boxes so they're thin, I leave the bottoms on.

If it's a log, it may be best to have an open hide. Plus make sure it only has one entrance, logs with open sides are bad, they stress out the snake.

Hope that helps.