Heated tobacco products (HTPs) such as IQOS have evolved across generations, with newer models using induction-based heating rather than a ceramic blade. Nicotine yields have declined across generations, raising the possibility that sensory characteristics have been modified to maintain product appeal. Current emissions assessments rely on standardized machine-puffing regimens derived from cigarette testing, which may not reflect real-world IQOS user behavior. This study will characterize puff topography (volume, duration, flow rate, inter-puff interval, number of puffs) in 50 exclusive IQOS users during ad-libitum use of the IQOS Iluma i and IQOS 2.4 under preferred and standardized (Amber) flavor conditions. A randomized crossover design with two visits will be used, with device order within each visit randomized using a Williams design. Secondary outcomes include chemosensory ratings (mouthfeel, ease of draw, throat hit), and subjective effects (satisfaction, pleasantness, taste, urges). Data will inform device-specific puffing regimens for use in future emissions assessments.