The design for what would be Milwaukee's tallest new office building in more than 20 years, set to be unveiled this week, combines two motifs that often compete: a high-rise exterior typically associated with staid finance and law firms and a large, open interior popularized by Silicon Valley.

Northwestern Mutual Life Insurance Co., founded in the 1800s, is building the $450 million, 32-story tower on its existing downtown campus near Lake Michigan. When completed, Northwestern Mutual's curved glass tower will be the state's...