We demonstrate the use of a 3D printed radial collimator in X-ray powder diffraction and surface sensitive grazing incidence X-ray diffraction. We find a significant improvement in the overall signal to background ratio of up to 100 and a suppression of more than a factor 3 · 105 for undesirable Bragg reflections generated by the X-ray "transparent" windows of the sample environment. The background reduction and the removal of the high intensity signals from the windows, which limit the detector's dynamic range, enable significantly higher sensitivity in experiments within sample environments such as vacuum chambers and gas- or liquid-cells. Details of the additively manufactured steel collimator geometry, alignment strategies using X-ray fluorescence, and data analysis are also briefly discussed. The flexibility and affordability of 3D prints enable designs optimized for specific detectors and sample environments, without compromising the degrees of freedom of the diffractometer.