This paper offers solution on how to predict the potential occurrence of condensation on outside surfaces of cold fluid carrying ductwork and piping and how to prevent it with the proper selection of insulation material and thickness. This is a perennial problem in hot and humid climates which has been causing tremendous loss of energy, damage to property that gets wet due to dripping that also causes the growth of harmful organisms, discomfort, loss of production in some cases, and expensive retrofits. This paper also gives a better understanding on how the difference in vapor pressures between the warm and humid ambient air and the cold surfaces that it surrounds is the vehicle that propels the flow of water vapor to the latter causing destructive condensation that wets, not only the insulation itself, but other materials as well. It is an attempt to correct the 'business as usual' practice of selecting and applying insulation on cold surfaces in tropical climates.