input: [0] Mild Steel [2] Easily available in every hardware store in 10 feet costs about $5 [3] Mild steel has the perfect amount of spring, [4] I would still be using this if it didn't rust. i used it for 10 years exclusively, it's a good metal to learn on. and you can dip it in lacquer to rust proof it. [1] 
output: Yes, it is firm, I tend to work in a 16 Gauge or below. It is not Especially brittle I can bend it back and fourth about 6 times