Yes, it's special. Very porous, so it hardly displaces anything. It just slows the flow enough that sloshing isn't as much of a problem. It also slows down leaks in the event of a wreck.
FUEL CELL SAFETY FOAM

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"When you find a big kettle of crazy, it's best not to stir it." - Pointy-haired Boss

1964 Valiant V200, 225/Pushbutton 904
BBD, CAI, HEI, LBP, AC, AM/FM/USB, EIEIO

I wonder how fast fuel is absorbed into the foam, and if there's a good way to adhere it to the metal of the tank...

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'74 Duster w/ HEI ignition, beat to snot suspension, A904, 8.25" 3.55 SG rear, still being tuned up and gets 17 MPG

Know how they always build a better idiot? That's me

Seems to me you are thinking of going to a great deal of trouble and expense to deal with a nonproblem. Turn the radio up and keep the tank full!

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

As a former Fuel Safe fuel cell owner I can say the fuel pours right through the foam. It's open cell to an extreme. You do not glue it to anything. Fuel cells are filled top to bottom, wall to wall with foam. It's not terribly cheap and it has to be replaced about every 5 years. Ask me about people not finishing races due to old foam.

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Joshua

Yeah I don't want something that's gotta be replaced on a regular basis, even if it is five years.

Dan, the sloshing drives me NUTS! Besides I like a challenge. And I won't have a radio until the car is almost completely restored and I can take it to the car stereo shop with about 3 grand and say "do me up". Oh yeah, and the guy builds competition systems for muscle cars, and specializes in Mopars

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'74 Duster w/ HEI ignition, beat to snot suspension, A904, 8.25" 3.55 SG rear, still being tuned up and gets 17 MPG

Know how they always build a better idiot? That's me