Although necessity remains the key driver behind men's shoe purchases, with two-thirds of men saying they shop only for replacement shoes, the boost is a signal that men are "becoming more interested in style and trends," said Marshal Cohen, NPD's chief industry analyst.
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"This is apparent by the growth of items such as fashion boots, drivers, sneakers and oxfords in various new materials and colors, which correlates with the growth of the men's apparel and accessories markets," Cohen said. "As men expand their wardrobes, they will need the right shoes to match."
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Despite outpacing the growth in women's, the men's footwear category still doesn't rake in as much money. In the past 12 months through May, women's footwear generated $28 billion, according to NPD. The men's market generated around $20 billion over the same period.
The growth in men's footwear mirrors that seen in the men's apparel market. According to a separate study by The NPD Group, men's U.S. apparel sales grew 5 percent in 2013 compared with the prior year, outpacing the 4 percent growth from the women's market.
The new study also found that men are more brand loyal than women when it comes to footwear. Nike, New Balance and Adidas topped the list for the top men's footwear brands.
—By CNBC's Krystina Gustafson