In Canada, and parts of the United States, most of the spruce tree species, pine tree species, and fir tree species share similar physical and mechanical characteristics, to the point where lumber derived from any of these species are interchangeable for construction purposes. Therefore, it makes sense to harvest and process them together, and sell them as one product.
On some exchanges, there are different prices for Eastern and Western SPF varieties, and the price of Eastern SPF is generally higher than the price of Western SPF. When both types are sold together, the term Composite SPF is used. There is also utility-grade SPF, which is the lowest and cheapest grade.