Purpose Foam Party Event What Is The Purpose Of The Strip Of Foam Attached To The Top Front Of The Radiator?

What is the purpose of the strip of foam attached to the top front of the radiator? - purpose foam party event

This strip of foam on the surface of the radiator is broken down and assembled has now disappeared. What it does and how important it is to replace it? Where can I get the foam? I (a Nissan Xterra) I