Innovation in firms is doubly embedded: in a social network of collaborations between researchers and in knowledge network composed of linkages between knowledge elements. The structural features of the two networks are distinct and influence innovation in different ways through separate mechanisms. Using patent data from a leading US microprocessor manufacturer, we constructed the firm's collaboration and knowledge networks and examined the effects of two structural features, structural holes and degree centrality, on researchers' exploratory innovation. The results show that a researcher with knowledge elements rich in structural holes tends to bring fewer novel knowledge elements to the firm, while structural holes in the collaboration network stimulate exploratory activities. The average degree centrality of a researcher's knowledge elements in the knowledge network has an inverted-U-shaped relationship with her exploratory innovation, while degree centrality in the collaboration network has a negative effect. These findings suggest that knowledge and social network structures influence where research scientists search for discoveries and their innovative productivity.