BEIJING — Dark, featureless, defiantly drab, it accompanies President Xi Jinping almost as constantly as his bodyguards.

Of the many mysteries about China’s president, the most evident may be the navy blue, zippered windbreaker that he wears like a second skin.

Mao popularized the tunic suit with a tight collar that now bears his name. Deng often wore the Mao suit, while his successors embraced Western business attire.

But Mr. Xi has become so attached to his windbreaker that it might now be called the “Xi jacket.”

On a recent trip to the countryside, he wore it next to a villager who appeared elated to meet the national leader while wearing a matching jacket. But he has also rocked the jacket in more formal settings, like a recent meeting in a Beijing lecture hall on the role of philosophy and the social sciences.