NNN agreement

A Western-style NDA mainly stops disclosure, but the bigger risk in China is that a factory uses your design or sells directly to your customers. An NNN covers non-disclosure, non-use and non-circumvention. It works best when written in Chinese, governed by Chinese law, enforceable in a Chinese court with jurisdiction over the factory, and with a clear liquidated-damages amount.

Sign it with the legal entity that will actually make the product, and sign it before you send drawings or samples. An NNN does not replace registering your trademark and, where relevant, patents in China. See OEM vs ODM.