Megna Pools COPDTRETSMWH 10' White Double Track Sidemount Retainer - MEGNA POOLS uses reliable and durable high-frequency molecular welds in the fabrication of all our pool liners. This process has been used in the industry for over 50 years and has proven to be the best and longest lasting method of sealing swimming pool vinyl. A high frequency molecular weld produces a seal stronger than the material itself!