Australia has unit supplying material for protective layer (5)
I believe the answer is:
ozone
'protective layer' is the definition.
(I've seen this in another clue)
'australia has unit' is the wordplay.
'australia' becomes 'oz' (informal name for Australia).
'has' is a charade indicator (letters next to each other).
'unit' becomes 'one' (synonyms).
'oz'+'one'='OZONE'
'supplying material for' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for ozone that I've seen before include "Ring" , "Sea-air" , "Sea air; bleaching agent" , "Bracing seaside air" , "lively atmosphere" .)