Aim: This project aims to design a lightweight, inexpensive and easy to use upper arm prosthesis through improving the design of ARM3D, which is a 3D printed body-powered transhumeral arm prosthesis. This study will cover general shortcomings of body-powered arm prostheses as the weight, cost, amount of parts and limited accessibility of them. This study also focusses on a natural appearance of the prosthetic arm. Results: The improved design of ARM3D is made of six 3D printed and eight non-3D printed parts. It has three Degrees of Freedom (DOF’s), one control cable, a harness both to suspend and control the prosthesis, an active voluntary closing hand, a passive rotating wrist joint and a passive elbow hinge joint. The prosthesis costs €59,68 and weighs 403 g. It takes 3 days, 6 hours and 47 minutes to print and 15 minutes to assemble. The maximum open hand width is 64 mm and the prosthesis needs 15 N of tension force on the control cable to operate. Furthermore, it is possible to paint the prosthetic fingernails and to remove the nail polish. Conclusion: An improved design of the ARM3D prosthesis is presented in this paper. ARM3D is almost entirely 3D printed. It is a lightweight and inexpensive device. A field study is required to gather more information whether the prosthesis is easy to use.