The present invention relates to thermally expandable microspheres at least partially prepared from bio-based monomers and to a process of their manufacture. The microspheres comprise a thermoplastic polymer shell encapsulating a blowing agent, wherein the thermoplastic polymer shell comprises a polymer being a homo- or copolymer of a lactone according to formula (1): wherein each of R1, R2, R3, R4, separately from one another, is selected from the group consisting of H and an alkyl group preferably with 1-4 carbon atoms. The invention further provides expanded microspheres, which can be used in a variety of applications.