This is an interesting question I haven't given much thought to before. In short, both mean the same thing, particularly when speaking about material items. There is a bit of nuance when using the former sentence to address a person, as we have been known to do in idiomatic expressions: "What are you made of?" "Show me what you're made of!" An athlete, for instance, might be "made of" resilience, passion, discipline, grit, and consistency. By contrast, what are athletes "made out of?" Muscle, bones, hormones, cartilage, blood, chemical compounds, the foods they eat, the drugs they take, etc. Made out of suggests a smaller component in general. Q: What is this shirt made of? A: Silk Q: What is this shirt made out of? A: 100% organic mulberry silk from California Q: What is silk made out of? A: The protein based silk threads from a silkworm It is a very delicate nuance. I'm sure others may answer more clearly, but that's my take as an American native-speaker of English.

Nothing. No difference and just play on words. That’s the English language for you.