Some electrical devices located in attics, generate lots of heat when operating. If you pile insulation on top of a heat producing fixture (HPF), it could get hot enough to start a fire. Before blowing insulation into an attic, place baffles around all HPFs.
Heat producing fixtures include most recessed lights and heaters, doorbell transformers, electrical wiring connections not in junction boxes, metal flues and knob & tube wiring. Heaters with an Underwriter’s Laboratory label that says “Heater” or “Air Heater” don’t need to be baffled. The same is true of newer recessed lights that are rated “IC,” which means they can be covered with insulation. They must have an identifying label. The label could also be on the outside of the housing, visible from the attic. If it’s inside the housing, you’ll have to remove the light bulb and maybe the trim piece that fits inside the housing to find the label. If you don’t see any of these labels, then you must baffle the fixture.
Baffles should be made from a solid, flame resistant material. Wide metal flashing makes a great baffle (except for use around wiring). It’s easy to bend, can be fastened with staples, and cuts easily with a utility knife. In some areas, fiberglass insulation batts can be used as baffles. Treated cardboard, sometimes used to baffle attic vents, is not acceptable for baffling HPFs. Baffles must be be firmly attached to something in the ceiling structure, such as the ceiling joists, rafters, or roof sheathing.
Read more at: http://oikos.com/library/weatherization/hpfs/hpfs.html