Injection molding of plastics requires metal molds, which can be manufactured with high precision and are adequate for producing thousands of parts. However, metal molds are expensive to make and time-consuming to machine. When the number of parts to be made is in the range of tens or hundreds, plastic molds made by 3D printing offer an inexpensive and rapid alternative. However, one challenge with plastic molds is their poor thermal conductivity, leading to slow production times. Hollow molds must be strong enough to withstand the molding pressures and rigid enough to meet the required geometric accuracy of the parts. In addition, hollow structures must allow cooling water to be pumped through them. One of the structures that meets the strength, rigidity, and free coolant flow is the column structure. For the mold material, we simulated the performance of 30% carbon filled Poly Ether Ether Ketone (PEEK) which is a carbon fiber-reinforced nylon compound that is both strong and fast cooling. The part being molded is cylindrical and is made of High-Density Polyethylene (HDPE) material. Our simulation results show that an adequately modeled hollow mold reduces the cooling time by more than 97% when room-temperature water flows through the mold. By using hollow molds, the volume of the mold and thus the cost and production time of 3D printing can be significantly reduced. In our example case, the hollow mold volume is 56% of the solid mold volume.