This study examines factors associated with the cavities formed in 3D-printed porous thermoplastics, and establishes their relationship with the thermal conductivity of bulk material. The research has examined two porous thermoplastics, specifically poly-lactic acid (PLA) and acrylonitrile butadiene styrene (ABS). Certain categories have been used for the cavities based on their shapes (sphere, cube and diamond), sizes (0.5 to 1.9 mm), numbers (200 to 500), and distributions (in-line or staggered). Specific findings indicate that the optimal thermal conductivity value can be achieved by utilizing samples with 500 pores of 1.5 mm pore diameter. It is shown, the pores could be in the shape of diamonds and distributed in a staggered manner in order to have minimum thermal conductivity. The thermal conductivity values for the most favorable specimens were determined to be 0.13 W/m·K for PLA and 0.12 W/m·K for ABS. The observed values demonstrate a decrease of 40-45% in comparison to the non-porous samples of the same materials.