Additive manufacture, specifically Fused Deposition Modeling (FDM), is an advancing manufacture method opening up new possibilities in design previously impossible to machine, in a relatively affordable way. However, its use in functional products is limited due to anisotropic strength and reduced strength from injection molded components. This paper aims to increase the tensile strength of Acrylonitrile Butadiene Styrene (ABS) in the weakest direction (Z axis), where poor interlayer fusion and air gaps between extruded trails reduce strength. Extra thermal energy was applied to the top surface layer during the printing process (through hot air) to encourage more polymer chain diffusion across the boundary, and spreading out to fill air gaps. Multiple tensile test samples were printed at a variety of heat levels. The ultimate tensile strength σuts was plotted against these temperatures and a weak positive correlation was found. However, only air temperatures above 81°C increased strength past the control to a maximum of 1.4MPa. Heat application has proven to increase tensile strength, but needs to be applied with a more precise method, to the boundary interface, to allow greater thermal energy transfer without sacrificing print quality.