Also called can lights, recessed light housing is available in two basic styles. New construction lights are bulkier and have a frame that can be affixed from above. New construction recessed lights are easy to work with when ample access is available from above, but are impractical when attic access isn’t an option. “Remodel” housing (shown here) is installed from below by wiring the fixture before pushing it in from below. Remodel housing is usually the easier option when replacing old fixtures.
You will also notice some housing is rated “IC” versus “Non-IC”. IC stands for “insulation contact” and has a greatly reduced risk of problems with heat and airflow when placed against insulation. When in doubt, select IC rated housing.