I used PLA. I made a set for him soon after getting my Snapmaker, but they were just simple wedges that raised the front of the foot 1/2". They used the standard infill setting and I thought they might be too weak, as well. They were not. They held up just fine for several months now. He is a C5 quadriplegic, and he uses a standing wheel chair, which allows him to achieve the standing posture so necessary for good health, periodically throughout the day. Even with his full weight (est. 135 lbs.) on them, they never broke or even cracked.
The version you see in the pictures is a new set that raise the front of his feet 3/4." Now that I am familiar with the CAD program I was able to custom build them to seat over 21 ridges running down the footplate plate (see pictures), and add bolt holes to secure it more firmly through the holes in the footplate (The original version used cable ties through holes I drilled into the wedges.) The print was done as a fast build, and I installed them about a week ago. So far PLA has not failed in the least.
Since these raise the front of his feet even more, I have been concerned that the infill (honeycomb, I call it) might make the build too weak, but so far, no problems. Were there to be a failure, I would not hesitate to try PLA again, though with a higher percentage infill and perhaps do a medium quality build