Provided herein according to some embodiments is polymerizable liquid useful for the production of a three-dimensional object by additive manufacturing, said polymerizable liquid comprising a mixture of: (a) at least one photopolymerizable component; (b) a photoinitiator; (c) at least one heat polymerizable component; and (d) heat expandable microspheres. A method of making a three-dimensional object from such a polymerizable liquid by additive manufacturing and objects so produced are also provided.