High-yield pulping, such as Chemithermomechanical Pulp (CTMP), is critical in developing sustainable fiber-based packaging materials. Achieving uniform lignin sulfonation during the impregnation process is crucial for maintaining fiber stiffness, maximizing bulk, and optimizing energy efficiency. However, current impregnation techniques often result in uneven distribution of sulfite (-SO₃⁻), leading to variations in fiber properties and increased energy consumption during refining. The ultimate goal is to achieve a middle-layer CTMP process that consumes less than 200 kWh/t of energy, significantly reducing the current energy consumption of 500-600 kWh/t [1].To improve process efficiency and create stronger, lightweight paperboards, gaining a deeper understanding of sulfonation at the microscale is essential. This study uses Synchrotron-based X-ray Fluorescence (XRF) techniques to analyze sulfur distribution in CTMP fibers with high spatial resolution (10–15 µm). By mapping sulfonate content at the fiber level, we aim to enhance impregnation strategies and ensure a more homogeneous sulfonation process. Our research has been validated at beamline facilities such as APS (USA) [2], Elettra (Italy), and Diamond (Oxford, UK), providing new insights into how sulfonate ions (-SO₃⁻) integrate into lignin structures, which directly influences fiber softening and defibration efficiency.We propose a refined impregnation approach that minimizes sulfite dosage while maintaining optimal fiber properties, ultimately reducing energy consumption in refining. By incorporating Synchrotron XRF analysis, we can assess the uniformity of sulfonation in wood chips in real-time, improving fiber separation and enhancing material performance. These advancements support the development of high-strength, lightweight packaging materials while promoting a more energy-efficient and eco-friendly pulping process. This study demonstrates the potential of advanced X-ray characterization techniques in optimizing the processing of fiber-based materials, bridging the gap between fundamental research and industrial applications. The findings contribute to the ongoing transition from fossil-based to sustainable, bio-based packaging solutions, aligning with global environmental goals.