If Frosty, Crystal, Milly, and Chilly wear them about their necks, they cannot melt.
8 seconds sound clip from the Rudolph and Frosty: Christmas in July movie soundboard.
You can hear this line at 00:25:52 in the Blu-ray version of the movie.
Quote context
[...]
- Wow. Like a Fairy Godfather.
- Oh, ho ho. Just say I'm an old, old magical friend who wishes to help.
- Children should see a circus at least once in their lives. So I will... help.
- But what can you do, sir, to stop Frosty and his family from melting?
- If Frosty, Crystal, Milly, and Chilly wear them about their necks, they cannot melt.
- Even though the temperature be hot enough to melt steel, still they will remain cool and icy.
- Wow! Our troubles are over forever!
- See. On each is a design. The letter F, four times entwined.
- Yeah! 'F', 'F', 'F', 'F'! What's that stand for?
- That means the amulet's magic only lasts until the final firework fades on the 4th.
[...]