What exactly is that orange/rust coloured insulation foam on the Space Shuttle external tank, the H-IIA/B, Delta-IV, and so many other launch vehicles? I remember finding the name of it in a NASA document somewhere but it has since escaped my memory (it was a combination of two different compounds if I remember correctly).

Note that I am asking what type of material this is, I understand very well the purpose of thermal insulation foam.

  • $\begingroup$ This is not very helpful, but in the industry it’s known as SOFI, for spray-on foam insulation. I know that sounds useless, but if you say SOFI (sounds like: Sofie) in the right circles, everyone knows what you mean. $\endgroup$
    – Adam Wuerl
    Nov 17, 2015 at 5:01
  • $\begingroup$ Thanks, the Shuttle ET document in the answer also mentions SLA ("slaw"). $\endgroup$ Nov 17, 2015 at 5:03

1 Answer 1


At least for the Shuttle ET:

The tank’s foam is a polyurethane-type foam composed of five primary ingredients: polymeric isocyanate, a flame retardant, a surfactant, a blowing agent, and a catalyst. A surfactant controls the surface tension of a liquid and thus cell formation. The blowing agent, HCFC 141b, creates the foam’s cellular structure by making millions of tiny bubbles or foam cells.


There are four specially engineered closed-cell foams used on the tank. The larger sections of the tank are covered in NCFI 24-124, which accounts for 77 per cent of the total foam used on the tank. NCFI 24-57, which has a slightly different formulation than NCFI 24-124, is used on the aft dome, or bottom, of the liquid hydrogen tank. PDL 1034, hand-poured foam used for filling odd-shaped cavities, and BX 250/265 foam is used on the tank’s “closeout” areas. During the early days of the External Tank’s development, PDL was an acronym for Product Development Laboratory, the first supplier of that foam. NCFI 24-124 and NCFI 24-57 are mechanically sprayed foams; BX 250/265 are applied mechanically on the feedlines and domes inside of the intertank and manually-applied, or hand-sprayed in the closeout areas.

Note: NCFI stands for North Carolina Foam Industries.

From here.


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