The transport mechanism of cell-penetrating peptides (CPPs) has not been fully understood and there seems no general rule to design more efficient CPPs. Recent experimental results show that a polyproline-containing arginine-rich peptide efficiently penetrates across cell membranes. We design a similar peptide in silico and study its efficiency using molecular dynamics (MD) simulations. We show how polyprolines change interactions between a CPP and a model membrane and we also compare free energy profiles (or potential of mean forces, PMFs) of translocation across the membrane.