AAA-137 2" x 4" x 12" SPF Lumber - SPF lumber is created by combining Engelmann Spruce, Lodgepole Pine, and Subalpine Fir wood to create a versatile and strong lumber. SPF can be used for many landscape projects because of its strength and ability to hold together with nails. The lumber is easy to cut and form together, making SPF lumber is the perfect framing option for any outdoor project.