Polar extremities, unfrozen - that's invaluable (9)
I believe the answer is:
priceless
'that's invaluable' is the definition.
(synonyms)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for priceless that I've seen before include "Totally absurd" , "Beyond value" , "Invaluable - very funny" , "Of incalculable value" , "Very precious; absurd" .)