From the website-
Explosion Suppressant Foam is reticulated polyurethane foam and is used in fuel tanks where the possibility of fuel tank explosion exists. Also known as ESF, or Safety Foam, the product was invented in the late 1960s when the United States Air Force began using reticulated polyester polyurethane foam to suppress fires and explosions inside fuel tanks.
Explosion Suppressant Foam has now been used for over 30 years and has found thousands of successful applications in aircraft, boats, military vehicles, competition and emergency vehicles.
Over the years the ESF for suppression of aircraft fuel tank explosion has evolved into seven generations of development often referred to as Type, for example Type 1 being the original polyester foam used by the USAF.
Each foam Type is qualified for all competition uses and approved by the FIM. This listing is for type 2 yellow foam.
Once installed inside the fuel tank the reticulated polyurethane foam essentially functions as a three dimensional fire screen. The foam is 98% void and only reduces fuel volume by 4% and adds only a negligible amount of net weight to the fuel tank.
I guess another benefit is that it could
possibly prevent rust forming in tanks because of the eliminated airspace when a tank is empty.
And another idea - it might also act as a fuel filter too, as the fuel goes in the foam would trap any medium to large particles.