Context: Organizations generate a number of solutions or ideas for a problem, by then select and synthesize some of these ideas for further development. Idea synthesis as an important phase of innovation process causes a reduction of enormous ideas to be considered by an interested company. Accordingly, innovation process can benefit from integration of ideas with restricted perspectives. Idea synthesis is effective when the defined product is novel, has high impact, is of low cost, and has good support from stakeholders. Idea synthesis is facilitated by the used of variety of structures. Interactive groups which require physical meeting of the participants are a facilitated forum for idea synthesis, where organizations try to utilize the multiple perspectives of groups. An alternative to this approach is bilateral communication between potential innovators. Bilateral communication is used by innovators that network with each other to identify related ideas and technologies in the context of open innovation. Software not only enables interactive groups and bilateral communication but also amplifies the performance of these structures by replacing them with online workshops or social networking. While both these structures are performed and justified through the use of software, it is not clear which of these structures is more effective. Objectives: The aim behind conducting this research is to compare the effectiveness of interactive groups and bilateral communication for idea synthesis. Additionally, besides the factors that affect achieving an agreement among the group members in both structures, a consistent pattern of idea synthesizing can be identified through the observation of participants’ behaviors,. Methods: In this study two research methodologies were used; a controlled experiment and a multiple-case study. First, an experiment was conducted to compare the effectiveness of idea synthesis of interactive group and bilateral communication channel for software product innovation. A total of 78 software engineering students generated software based solutions for a problem individually and subsequently combined their ideas to improve their initial solutions, either through the interactive groups or bilateral communication. Second, a multiple-case study using the collected data from the participants’ chat and questionnaires was conducted to identify the consistent pattern of idea synthesizing and the factors that affect achieving an agreement among the group members in both structures. Results: Statistical analyses of experimental results show no difference between interactive group and bilateral communication channels significantly for idea synthesis. It was found that the groups in bilateral communication channels could not generate more effective ideas than interactive groups in terms of novelty, feasibility, impact value, and stakeholder support through the ideas synthesizing. The identified factors which influence agreement among the group members, both challenges and determinants, in interactive groups and bilateral communication channels are categorized separately. Barriers in achieving an agreement between participants are included in context of ideas and participants’ interests in bilateral communication, while the barriers in interactive groups are features of ideas and participants’ features. Moreover, an agreement between participants is yielded in context of ideas and participants’ features in bilateral communication, while the agreement in interactive groups is yielded in context of ideas and participants’ interests. Conclusions: We conclude that there is no difference between interactive groups and bilateral communication for idea synthesis. The solutions achieved through both structures are not significantly different in terms of novelty, feasibility, impact value and stakeholder support. Moreover, achievement of an agreement in both structures not only depends on the context and features of ideas but also features of participants. On the one hand, the presence of ideas with consistent context and features besides motivated participants, interested in performing the idea synthesizing, lead to achieving an agreement. On the other hand, ideas with inconsistent context and features, lack of participants’ interest in sharing and synthesizing idea, lack of communicating, and lack of time managing hinder achieving to an agreement.