Please choose the correct solution to the question: For pocket-sized rice hand warmers, what kind of thread should I use?

Solution1: The thread must be 100% cotton so that you can heat it in the microwave. Polyester and other synthetics can burn or melt.

Solution2: The thread must be 100% polyester so that you can heat it in the microwave. Cotton and other synthetics can burn or melt.

Answer format: solution1/solution2
Answer: solution1