The outer layer of the example in the images is printed in Fillamentum Flexfill 98A Pistachio Green, which is an awesome and unique color that provides the perfect level of flexibility for this application. Get it here! Even though it was a 40 hour print in flexible filament, it worked perfectly with my Prusa upgraded with the Bondtech-Mosquito extruder-hotend assembly upgrade. In my opinion, this is the single best upgrade for your Prusa. The Bondtech Extruder and Mosquito Hotend are also very worthwhile upgrades by themselves. (affiliate links)
Rolling out your muscles has been shown (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4299735/) to reduce delayed-onset muscle soreness after a workout, improving performance and promoting muscle growth.
Unfortunately, foam rollers and other rollers like this one are often incredibly expensive (a quick google search brings up several results in the $30-$50 range). Printing this muscle roller is an easy alternative, and though it'll use up a decent amount of filament, it'll still be cheaper than buying an expensive one.
Having used both this 3D-printed one and a store-bought roller, I can confidently say that there's essentially no difference in experience. I included small ridges in a cool wraparound design that penetrate deeper into muscle tissue and improve results.
The outer layer, which I printed in semi-flex filament to make it more responsive, fits snugly onto the inner layer, which I printed in PETG to give it strength. It holds my entire body weight.
Check out my profile for the rest of my RECOVER series and for some other cool designs!