I am doing a cake for the 4-H fair. What should I use to make the decorations out of? I need something that will hold its shape for 7 days in hot humid weather.

Nothing I know of will hold up to 7 days of hot humid weather, unprotected. Gumpaste, pastillage, and royal icing can take a fair amount of heat, but high humidity will make them wilt after a bit.

That's what I was afraid of. I'm using a dummy cake so I don't have to worry about anything tasting fresh, I just needed the decorations to hold their shape. I have never worked with anything that would hold up for that long, just wasn't sure if anyone else had.

The best bet, I think, would be several layers of royal on the dummies, then royal icing decorations.