Most homes built after about 1985 feature adequate thermal insulation.  One of the more common upgrades to a home is "blown-in" attic insulation, and while thats a good thing to have when the house is built it's not going to return much value to have someone come out and add another 12" or so to the existing attic insulation. 

Typical fiberglass ceiling insulation works very well to protect against winter time thermal losses in fact the first 12" goes a long way.  In the summer when the roof is heated by the sun attic temperatures can reach over 180°.  An effective attic ventilation system can reduce the temperature by 50° or more.  One of the easiest systems to install are Turbine Fans and will generally pay for themselves in 2-3 months of reduced air-conditioning bills.

Hot roof surfaces also generate quite a bit of radiant heat that penetrates Fiberglass like water to a sponge.  90% of this radiant heat can be eliminated by covering the fiberglass batting with a paper thin radiant heat reflecting foil. 

Reflective Foil is a metal backed paper or plastic laminate that reflects radiant heat.  Radiant heat is what you feel from the sun for example, and all objects emit radiant heat.  The higher the temperature of an object. the more radiant heat it gives off.  Fiberglass insulation is practically useless to block radiant heat.  It may sound unbelievable, but a paper thin sheet of of reflective foil over the top of 18" of attic insulation will result in a 40% reduction of thermal loss. 

Reflective foil usually comes in 4" wide rolls and costs about $0.07 a square foot - 1000 square feet of attic space can be insulated for about $70.00.  Most homeowners can install this themselves in under an hour, and generally works out to 2 months or less payback in hot climates.

Installation of reflective foil is very easy that nearly every homeowner can do for themselves.

REFLECTIVE FOIL BENEFITS & INSTALLATION VIDEO

REFLECTIVE FOIL BENEFITS & INSTALLATION INSTRUCTION SHEET