A thermal sill will prevent heat or cold temperatures from transferring from the outside of the house to the inside of the house.  These conditions, such as condensation, can be eliminated with a thermal break in the sill, preventing the transfer of temperature and therefore further eliminating air and water infiltration into the home.

Non-Thermally broken options are available for moderate climates that do not have severe weather conditions.

Thermally Broken Z-Plus Sill                   NonThermally Broken
                                                                Z-Classic Sill