Protocol I on Non-Detectable Fragments prohibits the use of any weapon the primary effect of which is to injure by fragments which are not detectable in the human body by X-rays.[1][6] The reason is that such fragments are difficult to remove and cause unnecessary suffering. The protocol applies when the "primary effect" is to injure by non-detectable fragments and does not prohibit all use of e.g. plastic in weapons design.[7]