A December 23, 1997 report from Greg Katnik on a NASA site for kids and space enthusiasts: "During the STS-87 mission, there was a change made on the external tank. Because of NASA's goal to use environmentally friendly products, a new method of "foaming" the external tank had been used for this mission and the STS-86 mission. It is suspected that large amounts of foam separated from the external tank and impacted the orbiter."

He goes on to explain the process of investigation they used to examine the problem.
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North Carolina Foam Industries has a page describing the use of their foam on the external tank: "NCFI spray-applied foam insulation has protected the aft dome of the external fuel tank since 1983. Since 1998, NCFI foam insulates the entire tank."
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