Here is Leviticus 19:19: Obey my laws. Do not mate different kinds of animals. Do not plant your field with two kinds of seed.

Do not wear clothing woven of two kinds of material.

The word “polyester” is not in the Bible, but the synthetic fiber is made of more than one material--coal, air, water, and petroleum.

The Bible possibly forbids clothing that is all polyester. Anything mixed with polyester--say, cotton--is forbidden.

Deuteronomy 22:11 is more specific about what may not be mixed: "Do not wear clothes of wool and linen woven together.”

At our school, shirts are 65% polyester and 35% cotton.

Deuteronomy specifically forbids wearing a garment of wool and linen, but the Leviticus passage seems broader, forbidding clothes woven of two different types of fabric, no matter what the material.

Wool and linen would have been the options in the old days.

Woolen thread is from the hair of a sheep or goat (today it is made from a variety of other animals as well, such as llamas).

Linen was made from fibers contained in the stalk of the flax plant, as indicated by Joshua 2:6.

Cotton was not cultivated in that region.

The rule against wearing different types of fabric was not a moral law. There is nothing inherently wrong with weaving linen and wool together. 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 probably the key to understanding the prohibition. The ephod of the high priest was the SOLE garment that could be woven of linen and wool.

It is like anointing oil. God gave a special recipe for the anointing oil, and one may not duplicate the recipe for common use. No Israelite was allowed to make this oil for his own purposes (see Exodus 30:31–38).

Is it wrong for a Christian today to wear clothing made of two different types of material?

The prohibition was for ancient Israel, not for Christians who view the New Testament as holy scripture. The ceremonial laws for ancient Israel as recorded in the Old Testament do not apply today.

That law against mixing materials is from the Old Testament--the “old covenant.” The Old Testament doesn’t apply to Christians, who have a “new covenant.”

"Shatnez" is the name for this Biblical law forbidding garments containing a mixture of linen and wool.

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Leviticus 19:19 = Shatnez, Bible forbids polyester ("No clothing woven of two kinds of material")