The development of protective and safe textiles is of fundamental importance for defending the human body from bacterial infections. To this aim, garments are often functionalized with antibacterial agents. We recently started a program aimed at covalently linking antimicrobial peptides to cotton tissues. To optimize the process of binding, it is necessary to know the degree of functionalization and how deeply peptides penetrate into the cotton fiber. Here, we present a spin-label electron paramagnetic resonance (EPR) approach for obtaining data on the peptide incorporation into the fibers. The approach is based on the line broadening in conventional EPR and on the signal decays in electron spin echo spectroscopy that is a pulsed version of EPR.