Adam Clarke on Exodus 26:14

Rams' skins dyed red - See Clarke's note on Exo 25:5. This was the third covering; and what is called the badgers' skins was the fourth. See Clarke's note on Exo 25:5. Why there should have been four coverings does not appear. They might have been designed partly for respect; and partly to keep off dust and dirt, and the extremely fine sand which in that desert rises as it were on every breeze; and partly to keep off the intense heat of the sun, which would otherwise have destroyed the poles, bars, boards, and the whole of the wood work. As to the conjecture of some that "the four coverings were intended the better to keep off the rain," it must appear unfounded to those who know that in that desert rain was rarely ever seen.