In the case of recessed lighting, it is highly common for them to be designed to be Insulation Compatible (IC). IC essentially means that the fixture's housing is able to be installed with ease in direct contact with the insulation. Keeping this in mind, you should only purchase fixtures with housings that have an IC if you desire to put recessed lights into an insulated ceiling. When it comes to the colder months of the year, you'd want to make sure that heat remaining in your home instead of escaping through any entry ways. This is where Air Tight (AT) fixtures come in; having these help to keep warmth within your home when you most need it. This is also especially important for those typically unfinished parts of your home, like the attic. In addition to attics, if you want a recessed light for insulated attic, you should only purchase the fixture if is AT and IC rated. Luckily, a large majority of recessed lights come available in either one or both ratings.