Flex printed pressure-relief cushion

Personalized Pressure Relief Cushion: Solving Tailbone Issues

A friend of mine started having issues with his tailbone. His job requires a lot of sitting, and even with decent office furniture, he kept getting irritated pressure points. His doctor eventually prescribed a pressure-relief cushion, which did its job well from a medical point of view and definitely helped him

However, other issues started to appear. Heat and sweating became a problem because the prescribed cushion was anything but breathable. It also forced him into different sitting positions depending on the chair he used. Sitting at work became more comfortable, but when working from home, the curvature of his chair caused unpleasant pressure on his thighs

Since my job involves custom wheelchair construction, he came to me and asked if I could come up with something better — and that’s how this project started

Adaptive Geometry & Honeycomb Structure

First step was adjusting the cushion geometry so it matched his body more precisely. At the same time, we figured out how firm he actually wanted it to feel.

After optimizing the dimensions, I considered the simplest way to compensate for different chair curvatures. I decided to use a honeycomb structure. When properly oriented (90°), honeycombs have the ability to collapse laterally and adapt to the radius of the chair’s seat surface without significantly changing the overall shape of the cushion. This orientation is crucial for the targeted effect in the load direction

The Challenge of Firmness & Reliability

This is a very long print, so reliability beats experimentation. I needed a way to create different firmness levels reliably:

• Multiple Filaments? Without a TPU-capable multi-material printer, this would only allow layer-by-layer changes, making the print time even more impractical

• Infill Percentages? Since the finished print sees significant loads (often in shear), changing infill percentages could reduce layer overlap and introduce weak spots

The Solution: I settled on varying layer height, flow, and extrusion width. Using several modifiers, I defined zones with different parameters to control the mechanical properties

Technical Print Specifications

The print used a 0.6 mm nozzle and a default flow of 0.96.

• Base Layer: Honeycomb structure starting at 0.3 mm layer height, 8% infill, and 0.65 mm extrusion width.

• Transition: Up to 2 mm above the infill transition, I used a single perimeter. Important: The infill anchor must be set to 0 in perimeter-free areas to avoid serious stringing.

• Comfort Zone: I switched to an 8% gyroid infill for its excellent three-dimensional load behavior. The transition area used 0.2 mm layer height and 0.6 mm extrusion width to improve lamination.

• Finishing: Two mm later, I increased the layer height to 0.32 mm and reduced extrusion width to 0.6 mm to soften the structure.

I also added a small “roll” at the tuber edge to keep the cushion stable despite the steep seat angle

Results & Summary

After a long print time, the result was a success: everything fit, it felt good, and the gyroid structure was so comfortable through pants that no cover was needed.

Quick Summary:

• Flexibility Control: Managed via layer height, flow, and extrusion width for better adhesion and shorter print time.

• Base Structure: Orientation matters to properly handle load directions.

• Stringing Prevention: For perimeter-free printing, set the infill anchor to zero.

• Stability: Add a perimeter slightly above the infill transition for structural integrity.

Note: This is not a certified medical product. The design is personalized and would need adjustment for general use. Printed with Shore 95A. I will soon release a split, stickable version to make it accessible to a wider range of printers.

Happy flex printing!

UPDATE 1: Added a preview - next cushion about to be postet

UPDATE 2: V2 postet as a remix