 This summer, it's all about SPF, not sunscreen, two by fours. It stands for spruce pine fir, and it's the benchmark for lumber pricing in the U.S. Back in 2021, with demand soaring and supply chains a mess, the price peaked at $1,600 per thousand board feet, says Paul Yonke at Forest Economic Advisors. Prices currently stand at about $355. So lumber prices are extremely weak right now.