This work reports on the production of sustainable, cost-efficient food packaging films from unpurified agar-based extracts obtained from Gelidium sesquipedale seaweed. Unlike the purified agars, that required the addition of a plasticizer, the presence of impurities such as other polysaccharides (mainly floridean starch) and proteins exerted a plasticization effect in the unpurified agars, forming flexible films with no added plasticizer. The formation of interpenetrating polysaccharide/protein networks in the unpurified agar films had a positive impact in their mechanical and water barrier performance, which were similar or even better than those from the purified agars. Furthermore, these films showed improved resistance to high humidity conditions and retained their film structure, as opposed to the purified agar films, which gelled upon contact with moisture. Finally, the presence of impurities also provided the unpurified agar films greater light blocking capacity, inhibiting to a further extent the UV light-induced degradation of β-carotene.