Rapid Prototyped part failure constitutes a major issue for both RP providers and customers. When parts fail the reputation of the vendor is heavily deteriorated, customer dissatisfaction increase and replacement of the broken parts is often necessary to avoid the loss of future business. Product design teams often run into situations where Rapid Prototyped parts are not able to withstand shipping and handling and delivered broken or while demonstrating and examining the parts. When done in the face of customers this builds a perception of poor quality and lack of aptitude on the design group as well as the RP processes. The rapid advance of the RP industry and technology has led users to employ RP parts for structural applications where the need to understand in great detail and accuracy the mechanical behavior of the product and its individual components is greater than ever. Models built on Rapid Prototyping (RP) equipment are most often made from polymers which frequently have mechanical properties that are inferior to those manufactured by traditional methods such as thermoforming or injection molding. Not only are the mechanical properties of RP models typically low, they are usually, at least in thin sections, directly dependent on the section or wall thickness of the models. This dependence of strength on wall thickness makes it difficult to predict a proper wall thickness for RP models, even when nominal values of material strength are known. The purpose of this work is to present and compare measured values of tensile strength and stiffness as a function of wall thickness for three RP processes and materials. These properties will assist designers estimating adequate minimum wall thicknesses for models built by the three processes. The three RP technologies included in the scope of this research are: Z Corporation (powder with polymer binder layup), Fuse Deposition Modeling and PolyJet Layup (Objet). The findings of this study establish that tensile strength and stiffness values are dependent upon wall thickness, building orientation and direction of the applied force of specimens created with the methods in consideration. It was also determined that the correlation between thickness and strength for all processes is non-linear. Due to these results a single tensile strength and modulus value for each material and all wall thicknesses do not accurately represent their behavior. However, these results will allow a designer to understand the relationship between the wall thickness and using the data provided in this work be able to model and then fabricate adequate 3D prototypes.