Natural pine wood — the product details list them simply as wood (natural pine).
8 in × 1-1/4 in × 3/8 in — a full-length 8-inch shim dimension used across the listings.
They are tapered wedges — the standard wedge shape used for shimming and leveling tasks.
They are pre-scored so they can be snapped to the required length or cut to size.
Common uses include window installation and rough-opening leveling, interior and exterior door installation, cabinet installation and alignment, and general construction framing and leveling.