What are those things on wide receivers arms? I know its not tape, since I see a Nike symbol on them. It looks like tape wrapped around their upper elbow, but isn't.

its called a bicep band. does it do anything? i have no idea, but it does look cool.

it's material, sort of like under armor. It keeps sweat from there arms running down to their hands, making this slick. Slick hands makes it harder to catch the ball. Also helps keeps arms warm in the cold, and cool in the heat.