There are two passages in the Mosaic Law that forbid the wearing of different types of fabric; that is, the wearing of blended fabrics—those woven from two different materials.
“Ye shall keep my statutes. Thou shalt not let thy cattle gender with a diverse kind: thou shalt not sow thy field with mingled seed: neither shall a garment mingled of linen and woollen come upon thee.” Leviticus 19:19
“Thou shalt not sow thy vineyard with divers seeds: lest the fruit of thy seed which thou hast sown, and the fruit of thy vineyard, be defiled. Thou shalt not plow with an ox and an ass together. Thou shalt not wear a garment of divers sorts, as of woollen and linen together.” Deuteronomy 22:9–11
While the Deuteronomy passage specifically forbids wearing a woven garment of wool and linen, the Leviticus passage seems broader, forbidding clothes woven of two different types of fabric, no matter what the material. However, wool and linen would have been the primary options for the ancient Israelite when it came to making thread for weaving. Woolen thread would have been made from the hair of a sheep or goat, although today it is made from a variety of other animals as well (llamas, alpacas, etc.). Linen was made from fibers contained in the stalk of the flax plant (Joshua 2:6). There is no evidence that ancient Israel cultivated cotton, and of course they did not have synthetics like nylon or polyester. Therefore, wool and linen are in view in the Leviticus passage, even though the materials are not specifically stated.
Neither passage says anything about wearing two garments made of different kinds of material. For example, a linen undergarment worn with a woolen outer garment may have been acceptable. Nor do the commandments say anything about clothing that is not woven, such as leather or animal skins, being used with a lining made of wool or linen. The prohibition pertains only to wearing a single garment woven with both wool and linen.
The rule against wearing different types of fabric was not a moral law. There is nothing inherently wrong with weaving linen and wool together. In fact, the ephod of the high priest was made of linen and dyed thread (Exodus 28:6–8; 39:4–5). The dyed thread would have been made of wool. This fact is the key to understanding the prohibition. The ephod of the high priest was the only garment that could be woven of linen and wool. No one else was allowed to have such a garment. This rule was to place some distance between the high priest and the people, with the ultimate purpose of reminding Israel of how holy God truly is. A similar prohibition in the Law regarded anointing oil. God gave a special recipe for the anointing oil, and it was strictly forbidden to duplicate the recipe for common use. No Israelite was allowed to make this oil for his own purposes (Exodus 30:31–38).
The passages forbidding wearing clothes woven with wool and linen include a list of other prohibitions against mixing of various kinds. It is interesting to note that ancient Hittite laws also forbade the sowing of different kinds of seed in the same field. Mixing of this kind was reserved for sacred purposes, and the average person was not allowed to engage in these practices. In the Old Testament, the prohibitions may have been to maintain distance between the people and the high priest (and therefore God, whom the high priest represented). In other cases, the prohibitions may have been designed to keep the Israelites from imitating the superstitious or religious practices of the pagan nations surrounding them. Even though today, we do not understand all that is behind these prohibitions, we can be sure that the ancient Israelites would have understood exactly why the rules were in place.
So, is it wrong for a Christian today to wear clothing made of two different types of material? The clear and unequivocal answer is “no.” As we have seen, the prohibition was only for linen and wool, which would be uncommon today, anyway. Other types of blends were simply not in view. Beyond that, the prohibition was for ancient Israel, not for the New Testament Christian. The ceremonial laws for ancient Israel as recorded in the Old Testament simply do not apply today.