"粗纤维" in English can be expressed as "crude fiber" or "rough fiber" (though "crude fiber" is more commonly used in technical or scientific contexts). When referring specifically to "麻的粗纤维" (the crude fiber of hemp/flax), it can be translated as:
"crude fiber of hemp" (if referring to hemp fiber)or
"crude fiber of flax" (if referring to flax fiber, as flax is also a source of linen fiber).In a more general or less technical context, you might also see it described as "the coarse fiber from hemp/flax," but "crude fiber" is the standard term in many scientific or agricultural discussions.