Social media is transforming relations among members of parliaments, but are members taking advantage of these new media to broaden their party and ideological communication environment, or they are mainly communicating with other party members and ideologically aligned peers? This article tests whether parliamentarians' use of Twitter is opening communication flows or confining them to representatives of the same party or ideology. The study is based on a data set spanning the period January 1, 2013, to March 31, 2014, which covers all relations (4,516), retweets (6,045), and mentions (19,507) among Catalan parliamentarians. Our results indicate that communication flows are polarized along party and ideological lines. The degree of polarization of this network depends, however, on where the interactions occur: The relations network is the most polarized; cross-party and cross-ideological interactions are greater in the retweet network and most present in the mention network.