Children who experience greater math talk during home math activities demonstrate higher levels of math knowledge. The current study was designed to test whether the features of storybooks affect the amount and kind of extratextual math talk parents and preschool children produce during storybook reading. Parent-child dyads (N = 50) were randomly assigned to one of two conditions: implicit or explicit. The implicit condition involved a storybook with math elements embedded only in the illustrations; whereas, the explicit condition included the same set of illustrations as well as numeric and spatial words in the text. Both parents and children in the explicit condition produced more math-related utterances than those in the implicit condition. Among parents, the difference in quantity of talk was present across a range of different types of math talk. Mediation analyses showed that condition affected parent math talk via child math talk and child math talk via parent math talk. These results point to the bidirectional relation between parent and child math talk during storybook reading and the importance of the features of learning materials on that talk.