This paper gives an introduction to a new form of concrete called foam concrete which is manufactured by mixing a cement paste or slurry with a manufactured foam material. It is a revolutionary new cementing material which is both lightweight and strong. Here the technique of cast in-situ foam concrete preparation, use of fly ash as a filler material in foam concrete and a comparative study of heat insulation capacity of foam concrete to other commonly used construction materials has been presented. The paper discusses the changes in the property of foam concrete because of the use of different graded sands and different water-solid ratios. Its uses and advantages over other construction materials have also been enlisted.