What do you call this phenomenon?

I know what you’re talking about, but I don’t know a name for it. For me, it’s because I have extremely think, long, [veryyy] curly hair, and if I don’t wash it while camping for a few days or something like that, it doesn’t really get clean with only one shampooing because it’s so dried out and/or dirty that just one round of shampoo doesn’t quite cut it.

Can’t say that I have ever had this happen to me before, more than likely because I use 2 in 1, hair conditioner and shampoo. It usually works the way it should the first time.

I would venture a guess that it’s the oils that build up in your hair that prevent the suds from building up the first time through. After you rinse the first time, the oils etc. wash out, leaving clean(ish) hair. When you shampoo the second time there’s not as much oil that prevents a good lather from building up.

totally happens to me. wash, rinse, repeat as needed indeed!

Interestingly, sudsing supposedly has little or no effect on cleansing action of various types of cleaners (soaps, detergents, etc.). See www.bcscta.ca/resources/HebdenEnrichingChemistryTeaching.pdf
Hebden documents a case in which the public’s expectation of sudsing put a company out of business even though it offered a better cleaner. The company could never find any sudser (foam agent) to work with the cleaner. People would not buy it. But we all know the feel of clean hair and conditioned hair. This “cleaner” may not have been suitable for such cleaning tasks as shampooing hair. KAF, Chemist

Just for fun. Visit Theodore Gray’s http://periodictable.com for photos of the elements and fascinating facts about them.

I would say it’s probably because of all the grease that has appeared in your hair over the last few days creating more of a shield against the shampoo. This would make it less likely that the shampoo would be absorbed and go frothy.