A Canadian specification originally, SPF is a mix of Spruce, Pine and Fir growing in different regions of the country. The mix of these 3 species yield high grade timber with somewhat small, sound and tight knots. While SPF grown in East Canada offers better strength, it is the Western grown SPF that is more widely available as it grows much faster.
The most common Western species are White spruce, Engelmann spruce, Lodgepole pine and Alpine fir.
SPF has excellent thermal performance, is extremely dimensional stable especially given the special heat-treatment applied to most grades. It is also highly durable and versatile and has an excellent strength to weight ratio.