The primary cell wall (PCW) is a key dynamic extracellular matrix established as a major regulator of plant development¹. PCW provides both structural support and plasticity, enabling controlled cell expansion during growth. The PCW is composed of polysaccharides (∼90%) and proteins (∼10%). EXTENSINS (EXTs) are described as structural proteins, yet their roles during cell growth are still poorly understood. Here, we explore the formation of EXTs-based networks and their roles during cell growth. Functional studies of this protein family remain challenging due to their biochemical and genetic complexity. We focused on the elongating Arabidopsis thaliana root hairs to bring functional insights into their characterization. Short root hairs were reported in mutants for some AtEXTs genes. In this work, we used ext12 mutant lines in complementation experiments, alongside with wild-type (WT) plants for overexpression experiments. We cloned EXT12 under the control of either strong or native promotors. The complementation effectiveness was assessed by root hair length measurements and shape evaluation. Different levels of complementation were observed. The tissue specific expression was analyzed in WT plants transformed with promoter activity reporter constructs. We also assessed pEXT12::EXT12-tagRFP sub-cellular localization in complemented ext12 mutant background.