Background and purpose: ProSpare is a self-insertable rectal obturator which can reduce motion error and anorectal dosimetry in prostate radiotherapy. It is being evaluated in the post-operative setting where 7/19 (37%) patients could not insert the device. Endorectal balloons are commonly used in prostate and post-prostatectomy radiotherapy and have good tolerance because they are inflatable. The aim was to create an inflatable device, like ERBs, which expands to become rigid and angled to act as a rectal stabiliser like ProSpare. Materials and methods: Devices were made using a custom laser welding system developed at the Hamlyn Centre, St Mary’s Hospital. This was followed by laser cutting and soldering to create the 3D shape. A three-sided and four-sided dual-truncated prism design and a three-sided reinforced actuator design were explored. Devices were inflated using a pneumatic compressor and their rigidity tested by tactile examination. Burst testing was followed by increasing the pressure 0.1 bar at a time on the pneumatic compressor. Minimum and maximum dimensions of the devices while folded/deflated and deployed/inflated were measured, respectively, to obtain expansion ratios by volume. Results: The three-sided dual-truncated prism design could not be folded but the four-sided device could. However, the four-sided device would push against the posterior anal wall during deployment. The reinforced actuator design was more successful: it could be folded and had an expansion ratio of 14.7 by volume and reached an angle of 20° on inflation. Its chambers started inflating, became rigid, and burst, when the pneumatic compressor reached 0.5, 1.0, and 1.6 bar, respectively. Conclusion: A device capable of inflating and deploying to become angled and rigid was created. The next steps include exploring ways to increase the angle, directly comparing rigidity to ProSpare with a force sensor, and adding steel discs so the device acts as an IGRT tool.