Fenical Bump Cap Insert-Outdoor Safety ABS PP Foam 4-hole Bump Cap Insert for Baseball Caps (Black) Color: Black. Material: Hard ABS, soft PP foam. It has air holes on the cap for ventilation. Fits inside most "high profile" or "pro style" baseball caps. Ideal for protecting head from lacerations, minor bumps and bruises in areas that do not require certified safety helmets. Lightweight working cap is great for full time outdoor workers in the low-risk workplace.