Material in Missouri musical (6)
I believe the answer is:
mohair
'material' is the definition.
(mohair is a kind of material)
'missouri musical' is the wordplay.
'missouri' becomes 'mo' (abbreviation for the US state).
'musical' becomes 'hair' (1960s musical).
'mo'+'hair'='MOHAIR'
'in' acts as a link.
(Other definitions for mohair that I've seen before include "Cloth made from wool of angora goat" , "Angora fleece" , "Fabric from coating of angora goat" , "Fabric made from silky hair of angora goat" , "Fabric made from the coat of an Angora goat" .)