Non-IC light housings are for use in areas where they do Not make direct contact with ceiling insulation. If your application requires the housing making direct contact with insulation, purchase housings that state they are "IC" rated.
This means that these housings can NOT make direct contact with
insulation. Some codes allow you to use and space the insulation 3" away
and some codes do not allow you to use NON "IC" Housings at all
if insulation is present. These housings are still used because they usually
allow for higher wattages, but now with the introduction of the new
"IC" Air Tight housings that can handle the same higher wattages,
these non "IC" housings are being phased out of the industry.