Plastic glasses are known for their durability and optical performance. They are also lightweight and come in a variety of shapes, sizes, colors and styles.  Like other frame materials, plastic glasses may need adjustments now and then for that perfect fit. Here are some ways to tighten plastic glasses for wearers of all ages:
You can heat the temple tips with a hair dryer or hot water for 20 seconds if the glasses are too tight or loose.
Hold the plastic glasses by the nose piece and gently bend the temple tips.
Adjust the nose pads (if available) by bending them outward if the glasses are sitting too high. Bend them inward if the glasses are sitting too low.