This paper investigates what types of Instagram marketing tools are the most effective in relation to Generation Z's impulse purchasing behaviour within fashion industry in the context of the United Kingdom. The research applies Stimulus-Organism-Response model to the context of Instagram. The findings of this qualitative study based on eight extensive focus groups conclude that there are significant gender differences in relation to impulse purchasing behaviour on Instagram. Instagram is vastly influential in encouraging impulse purchases amongst females, however, this was not the case for male participants. A revised Stimulus-Organism-Response model is proposed to Instagram, concluding that advertisements, opinion leaders and user-generated content act as stimuli (S) in evoking positive emotions (O), which subsequently trigger impulse purchases (R) in Generation Z females.