Yes, ceiling insulation is effective in keeping heat out, especially during the warmer months. It acts as a barrier that reduces heat transfer between the inside of a building and the external environment. By insulating your ceiling, you can maintain a cooler and more comfortable indoor temperature in the summer, reducing the need for excessive air conditioning. This not only enhances comfort but also contributes to energy savings. Remember, the effectiveness of the insulation in keeping heat out depends on the quality of the material used and proper installation.