If not glass then Polycarbonate - definitely.
Most other clear plastics are thermoplastic - meaning they would melt from the heat. Polycarb is Thermoset - but may discolour under extreme heat or even bubble and char.
Lexan is a good start - but you could also try products called Makrolon or Rigidex.
Maybe a hard coating could be applied to stop scratching - like with spectacle lenses?
FWIW Tempered glass isnt expensive as long as it is flat.
Phil
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