Charles Ellicott Commentary Leviticus 16:4

"He shall put on the holy linen coat, and he shall have the linen breeches upon his flesh, and shall be girded with the linen girdle, and with the linen mitre shall he be attired: they are the holy garments; and he shall bathe his flesh in water, and put them on." — Leviticus 16:4 (ASV)

He shall put on the holy linen coat. — Better, a holy linen tunic. The four articles of clothing mentioned here, all of which were of white linen, constituted the sacerdotal “white vestments,” in contrast 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. He could also 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 that the high priest wore on this occasion. He put these on later in 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 he changed his vestments.