The polycarbonate pieces clip into the grille and block cold air from entering the radiator and engine compartment. I used these for several winters in Colorado on our '94 Suburban and they did a great job of getting the heater fired up sooner. Alas, there isn't much need for them here in Central Texas. 
They're described here and fit trucks with the grille style in the top pic here.
$25 plus shipping.
They're described here and fit trucks with the grille style in the top pic here.
$25 plus shipping.
