What we learned With our climate partner, Cooler (climatecooler.com), we analyzed the carbon created in making and shipping a typical leather midcut (it’s 150 pounds per pair), then compared the five boots here based on data from their makers. For a normal boot, 70 percent of the impact comes in manufacturing and assembling the parts; 27 percent is from transportation and energy use at stores and company offices.
The manufacturing portion breaks down into three major components: fossil fuel consumption (56 percent), nitrous oxide from fertilizer production and manure (23 percent), and methane released from … you guessed it, cow farts (18 percent). Two of the three manufacturing processes relate directly to leather production, which emits significantly more carbon than other upper materials. According to Cooler, leather has five times the impact of nylon and 30 times the impact of recycled PET (plastic from milk jugs). Assuming an equal lifecycle for leather and comparable synthetics, manufacturers could cut the footprint of leather boots by 35 percent just by using nylon. (We assumed an equal lifecycle based on our field-testing; we’ve seen no significant durability difference between leather and synthetic uppers of similar weights. We’ve also found that midsoles and treads typically wear out before uppers do. Not everyone agrees that synthetics are better, though, including Patagonia.)