Long-lasting insecticidal nets are recommended by the World Health Organization for malaria vector control. They contain insecticidal molecules which should be present at the surface of the net to be effective. The control of the insecticide migration within the yarns is thus of major importance in net production. Many scientific works studied nets efficacy based on bio-assays although only few of them tackled migration issues. The purpose of this study is to understand the influence of the fiber processing on the migration of insecticide molecules within the polymer matrix. We considered insecticide molecules of the pyrethroid class incorporated in a polyethylene matrix. Yarns were manufactured in the laboratory focusing on three key-steps (spinning, post-stretching and annealing). Influence of each step on yarn properties was investigated using tensile tests, differential scanning calorimetry and wide-angle X-ray diffraction. The post-stretching step was proved to be critical in defining yarn mechanical and structural properties. Even though a first orientation of polyethylene crystals was induced during spinning, the optimal orientation was only reached by post-stretching. The results also showed that final annealing did not significantly change these properties. A new titration method based on gas chromatography was set up to assess the resulting insecticide concentration in the yarn. The presence of insecticide molecules at the yarn surface was evidenced by scanning-electron microscopy. The fractions of insecticidal molecules located within the yarns and at their surface were measured quantitatively thanks to successive solvent washings. These studies performed at each fiber production step allowed a detailed analysis of the insecticide location and migration. It is concluded that while post-stretching decreased the migration rate, annealing seems to boost this migration.