Leviticus 16:4

He shall put on the holy linen coat. — Better, a holy linen tunic. The four articles of clothing here mentioned, all of which were of white linen, constituted the sacerdotal “white vestments,” in contra-distinction to “the golden garments.” Of the white garments he possessed two sets, one of Egyptian linen, and the other of Indian and less costly linen. The community allowed the high priest thirty minæ to purchase these garments, and he could add as much as he liked from his own money if he wished them to be more costly, provided the material was linen made of six double twisted threads and of flax. It was the more costly vestments of Egyptian linen which the high priest wore on this occasion. The latter he put on in the after part of the day when he entered the Holy of Holies to bring out the censer. These garments were the same as those of the ordinary priests, except the turban, which was a little taller.

And he shall wash. — He had to bathe his body every time when he changed his vestments.