Continuous manufacturing is an emerging technology in secondary pharmaceutical manufacturing of oral solid dosage forms such as tablets. Continuous blending is a crucial process step in continuous manufacturing. Residence mass (i.e. fill level or hold-up mass) is a critical process parameter of continuous blending and it is defined as amount of material in the blender at controlled state conditions. Residence mass affects for example on the blending efficiency and the residence time distribution. Aim of the study was to elucidate the characteristics of residence mass and its implications. Results showed that residence mass can consist of proportions that are involved in blending process (i.e. effective residence mass) and proportions that are not involved in the blending process (i.e. dead mass). The dead mass has several implications related to the quality attributes of the finished product, detection and segregation of nonconforming material and raw material traceability. (C) 2019 Elsevier B.V. All rights reserved.