i use thin plastic sign material ,cut 2" wide and then to whatever length of the barrel . the other one is old window blinds , as they have a curve to the material , its normally thin Gauge Aluminum , again 2" wide and is easy to cut .
attach with small velcro dots to the barrel .
other shooters are using portable fans , they are the recharge type and sit on the bench blowing down the length of the barrel . i have a small fan it works okay , but i seem to go back to the shield .
hope this helps , Steve .