Vacuum venting has been reported to be an effective technique in replicating micro-features by micro injection moulding. High surface-to-volume ratio and reduced dimensions of micro-parts promote the instantaneous drop of melt temperature and consequently lead to incomplete filling. This study aims to investigate the effects of variotherm process, cavity evacuation and their interaction on the production of a microfluidic filter for biomedical applications. The aspect ratio achievable in replicating micro features is one of the most important process characteristics and it is a major manufacturing constraint in applying injection moulding in a range of micro engineering applications. A low-viscosity polystyrene and a cyclic olefin copolymer were moulded applying a combination of mould evacuation and a rapid mould temperature variation that keeps the cavity temperature above the glass transition temperature during the injection phase. The research revealed the importance of these moulding technologies in enhancing part filling and the replication quality for high aspect ratio features.