THE INNER GARMENT - TUNIC OR SHIRT
The tunic (often translated "coat") was a shirt which was worn next to the skin. It was made of leather, haircloth, wool, linen, or in modern times, usually of cotton. The simplest form of it was without sleeves and reached to the knees or sometimes to the ankles. The well-to-do wore it with sleeves and extending to the ankles. Women as well as men wore it (see Song of Solomon 5:3), although there was no doubt a difference in style and pattern in what was worn by the two.
Among the lower classes, the tunic was often the only dress worn in warm weather. Persons of higher rank might wear the tunic alone inside the house, but would not wear it without the outer garment outside, or when they were to receive a caller. In the Bible the term "naked" is used of men clad only with their tunic (cf. Isaiah 20:2-4; Micah 1:8; John 21:7). To be dressed in such a scanty manner was thought of as "nakedness."
As a rule the Jews of CHRIST's day had at least a change of apparel. A man would be considered poor to have only one garment.
Yet John the Baptist said to those who heard him, "He that hath two coats, let him impart to him that hath none" (Luke 3:11). And when JESUS sent out the Twelve on a preaching and healing mission, He told them not to take an extra undergarment with them (Matthew 10:10).
The apparel which Jacob gave to Joseph (Genesis 37:3) is rendered in our English translations, "coat of many colors." But the Hebrew expression here is the same as the one used for the garment worn by Tamar the daughter of King David, and translated in the Greek and Latin, "a sleeved tunic." (See II Samuel 13:18) For this reason many Bible scholars believe it was a long undergarment with sleeves: The working classes usually wore a short tunic, whereas the aristocracy wore a long tunic with long sleeves. Thus it would be a mark of distinction for Joseph to wear the latter. But some are inclined to think it was a robe worn over the tunic.
The garment of JESUS for which the Roman soldiers cast lots was a tunic without seam (John 19:23). It has often been referred to as a robe, but this is not correct, for it was not His outer garment, but rather His undergarment.
[Manners And Customs of Bible Lands]