Charles Ellicott Commentary Exodus 26:12

"And the overhanging part that remaineth of the curtains of the tent, the half curtain that remaineth, shall hang over the back of the tabernacle." — Exodus 26:12 (ASV)

The remnant that remains. —Even after the doubling back, the goats’-hair covering would be half a breadth wider than the linen one. This half-breadth was to be allowed to hang down at the back of the tent.