This depends more on the material and less on the topper itself. The Emma Premium Topper, for example, has heat-conducting properties that help the body reach the ideal sleeping temperature in the shortest possible time.
Toppers made of Airgocell foam, such as the Flip Topper, also reduce increased sweating because of their open pores. The materials have a restoring force and so the body is not so strongly absorbed by the sleep system.
Viscoelastic foam is an exception to this rule. This foam reacts not only to pressure, but also to heat which makes it more elastic. Due to the high density of viscoelastic foam, you would sleep hotter on a topper made of pure visco foam.