Thermoforming is a classical polymer shaping process, but it does not easily allow designing complex shapes, on the contrary to 3D printing (or Polymer Additive manufacturing (PAM)). Among all 3D printing techniques, Fused Deposition Modeling (FDM) is of high potential for product manufacturing, with the capability to compete with conventional polymer processing techniques. Currently, classical FDM is a quite low cost technique, but the range of filaments commercially available is limited and costly. However, in some specific 3D printing processes, no filaments are necessary. Polymers pellets feed directly the printing nozzle, allowing to investigate many polymeric matrices, with no commercial limitation. This is of high interest for the design of flame retardant materials, but literature is scarce in that field. In this work, a comparison between thermoforming and 3D printing processes was performed on both neat Ethylene-vinylacetate copolymer (EVA) and EVA flame retarded with Aluminum TriHydroxyde (ATH) at different loadings (30 or 65 wt%) or Expandable Graphite (EG), ie. EVA/ATH (30%), EVA/ATH (65%) and EVA/EG (10%), respectively. Morphological comparisons, using microscopic and electronic microprobe analyses, revealed that 3D printed plates have lower apparent density and higher porosity than thermoformed plates. The fire retardant properties of thermoformed and 3D printed plates were then evaluated using Mass Loss Calorimeter (MLC) test at 50 kW/m2. Results highlight that 3D printing can be used to produce flame retardant systems exhibiting similar or even better flame retardant properties than the thermoformed ones. This is a pioneering innovative study for exploring the feasibility of using PAM technology for designing new and efficient flame retarded materials and it offers the way to make safer materials at low cost.