This study examines the ability of reactive multilayer foils to generate heat as a function of magnesium composition. This is accomplished by comparing the heat generated from the reactions of three chemistries: Al:Zr, Al-8Mg:Zr, and Al-38Mg:Zr, which correspond to foils with alternating aluminum and zirconium layers where the Al is either pure, an 8 at.% Mg alloy, or a 38 at.% Mg alloy, respectively. We have found that Al-8Mg:Zr releases 53% more heat than the Al:Zr foils when reacted in air (from 2.5 kJ/g for Al:Zr to 3.8 kJ/g for Al-8Mg:Zr), and 28% more heat than Al-38Mg:Zr (3.0 kJ/g), based on measurements performed in a specially designed bomb calorimeter. This may be a result of the expulsion of particles and vapor which is unique to the Mg-containing foils, because the increase in surface area enhances combustion. In order to understand this mechanism more thoroughly, the ejected particles, ejected vapor, and remaining foils were all characterized to understand the amount and composition of all species being ejected, and how that influences the combustion of each foil.