Pinit Backings for First Day Covers. U.S. Cover #10 Envelope. 4-1/4 x 9-3/4". .028" thick Acid Free Board. Long-term Storage. SKU: KAF28US10 (0)No Reviews yet Add to Shopping Cart Details Backings for First Day Covers - U.S. Cover #10 Envelope. 4-1/4 x 9-3/4" .028" thick Acid Free Board. Board is white on both sides. Use for Long-term... Details Back DetailsBackings for First Day Covers - U.S. Cover #10 Envelope. 4-1/4 x 9-3/4" .028" thick Acid Free Board. Board is white on both sides. Use for Long-term Storage. Reviews 0 Back Ratings & ReviewsNo reviews availableBe the first to Write a Review