Temperature aside, glass is protecting hot young flyer (9)
I believe the answer is:
chrysalis
'young flyer' is the definition.
(young butterfly or moth)
'temperature aside glass is protecting hot' is the wordplay.
I cannot quite understand how this works, but
'is' is found in the answer.
'hot' could be 'h' (abbreviation eg on taps) and 'h' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for chrysalis that I've seen before include "insect developing" , "Hardened pupa of butterfly" , "Dormant insect pupa" , "Cocooned pupa of a moth or butterfly" , "Pre-butterfly stage" .)