The weight of leaded glasses is directly related to the amount of lead used in their production. Leaded glasses are made of a combination of glass and lead. The glass provides optical clarity, while the lead blocks the harmful ionizing radiation. The higher the lead content, the heavier the glasses. 

Lead glasses contain lead oxide,  a compound with the heavy element lead in it. As a result, the lenses of leaded glasses are extremely dense, making them heavier than regular eyewear.

Another reason for the increased weight of leaded glasses is that they typically have larger lenses. These lenses offer a wider coverage area, making them more effective for protecting the wearer’s eyes from radiation exposure. However, the larger lenses also mean that there is more heavy lens material in the glasses, resulting in a heavier overall weight.

To further enhance the grip of lead safety glasses, they are equipped with high-friction nose pads and/or temple pads that prevent them from slipping off the face. In addition, they typically come with some sort of lanyard or holding strap to keep the glasses securely in place.

It’s worth noting that lead lenses are usually composed of about 70% PbO, and they typically attenuate x-ray radiation as well as or better than a 0.75mm thick sheet of pure lead. These glasses are essential for individuals who work in radiation-related fields, and are a necessary safety measure to prevent eye damage caused by radiation exposure.