The antonyms for the word "more heavy-duty" are "less severe," "lighter," and "weaker." These words denote a decrease in weight or intensity, as opposed to an increase, as in "heavy-duty." "Less severe" suggests something that is less intense or rigorous, while "lighter" denotes a lower weight or pressure. Lastly, "weaker" implies a lower strength, force or intensity. These antonyms may be used when comparing different products or materials that have different levels of durability or strength. Choosing the right antonym can help to convey the intended level of intensity or strength in a given situation.