It is a type of material that stretches and is used especially for making clothes fit tightly.
Flexfit 5001 - 6-Panel Structured Mid-Profile Cotton Twill Cap
Flexfit 6477 - Wooly Blend 6-Panel Cap
Flexfit 6277 - Wooly 6-Panel Cap
Flexfit FF6477 - Wool Blend
Flexfit 180 - Delta Seamless Cap
Richardson 110 - Fitted Trucker with R-Flex Cap
Flexfit 6277Y - Youth Cotton Blend Cap
Gildan G186 - Heavy Blend™ 8 oz., 50/50 Full-Zip Hood