There is no requirement for "absorbtion" in any rule book I have ever read, but I sure haven't read them all

I understand that they may be required to "contain" a certain volume of liquid. Hell, I don't know, really, but in CCS, it says:
[i]"5.2.23 All 4-stroke machines must be equipped with a fluid catch pan of sufficient size
and heat-resistant material to contain the contents of the crankcases in the event of
an engine or crankcase failure. Minimum capacity of the fluid catch pan is to be 3
quarts.
A. Enlargement and/or modification of an OEM fairing lower is permitted to attain
the necessary fluid retention
B. Machines not equipped with a lower OEM fairing may install a fairing in order to
comply with this rule as long as it meets the minimum requirements in Section
5.2.11 of the rules.
C. A maximum of two holes, 1" or smaller in diameter, may be drilled in the fluid
catch pan. These holes are to be plugged during dry conditions, and may be opened
only when the event is declared “wetâ€Â