When my mate put a plastic water pipe, in the same indoor rated pipe insulation outside to his shed, he didn't suffer freezing, but the birds pecking at it pulling chunks away.
Not too sure if they actually flew away with what they pecked out or just dropped it in the garden or were just being spiteful for using the wrong insulation type.😉 Anyway replacing with an outdoor rated insulation, which has an outer plastic shell, spoilt all the birds fun. He did suffer freezing pipes, but being plastic didn't leak when thawed.