The Skullerz 8945 Universal Bump Cap Insert is a lightweight, impact-resistant shell that easily inserts into any baseball cap, hat or other headwear for protection against bumps, scrapes, bruises and other minor head injuries. With flexible sides and convenient trim-to-fit customization, this bump cap insert easily fits a variety of hats/caps and head shapes. The shell is made of lightweight, durable polypropylene and designed with maximum ventilation for breathable airflow that doesn't compromise protection. An interior foam pad reduces impact but does not absorb odors for fresh all-day wear.