A lightweight thermoplastic is a type of plastic that is lightweight and has a low melting point. The three crossword solutions for this term are Saran (5 letters), BALSA (5 letters), and PANAMA (6 letters). Saran is a type of polyvinylidene chloride, which is a synthetic resin used in food packaging. BALSA is a type of wood that is light and strong, often used in model airplanes. PANAMA is a type of straw hat that is lightweight and breathable.