Insulatle is learned by Priests and Sages at level 32, and costs 6 mp to cast. In the original version the spell will reduce damage by 33%, overriding any additional reductions provided by armour. This bug is fixed in all subsequent versions, and the spell will last 6~9 turns in all versions.
Insulatle is learned by Meena at level 29, and costs 6 of her magic points to cast. It reduces damage by 50%, setting the precedent for nearly all future appearances.
Interestingly, Insulatle decreases breath damage by a massive 70% in the original Super Famicom version. This is likely the reason why armour resistances are weaker than usual in V.
This spell is obtained by advancing to Rank 2 of the Sage vocation, and once more costs 6 MP to cast.
Insulatle is learned by Jessica at level 25.
Insulatle is learned by rangers at level 26 and priests at level 43. It reduces breath damage by 25%, capping at 50% when cast twice, and costs 8 mp to cast. The affects of the spell will last for 6~9 turns.
Insulatle (then Barrier) is learned by monsters beginning at level 18 if the monster has at least 76 MP and 70 Intelligence. It is learned naturally by AmberWeed, KingSlime, MistyWing, WeedBug, and WindMerge. 
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