"Reinforce gel" by Mack's (or Mack's Professional) refers to a line of builder gels designed to strengthen natural nails and provide a foundation for nail extensions, overlays, or repairs. These liquid or builder gels offer a stable, self-levelling formula that is easy to work with for nail technicians. The product is used to add hardness, durability, and length to nails, and it's cured under a UV/LED lamp.