I use this in the work place to protect my head from minor bumps. Not a replacement for helmets.
Bump Cap Inserts (affiliate): amzn.to/3lrQQxB
Universal safety bump cap insert it is lightweight and fits into any baseball hat. Skullerz. You can trim use scissors to trim cut it to fit different caps. Lightweight polypropylene construction will not break or crack. Breathable vents allow for airflow.