Pyrex and glass dildos are a type of artistic sex toy that is very well known and popular, the sex toy made of glass art. Don't worry, this glass won't cut you or shatter on use, in fact most glass sex toy manufacturers don't even use pure glass anymore, they use Pyrex glass. Most manufacturers in general that make things out of glass, such as kitchenware, have changed to Pyrex glass, this is due to the fact that it is more resiliant to tempurature changes and breaking.
Glass dildos, or pyrex dildos, are used for many reasons, one reason is there purely artistic sexual beauty. However they also serve a very functional purpose over standard dildos of the same use. Glass dildos are very very hard and extremely smooth, the smoothness provides a comfort when in use and the strength means you receive the full potential of its ability without any give.
But don't think that glass dildos and pyrex dildos come in the standard shapes and sizes only. You can find many different styles for vaginal stimulation, including solid, smooth shafts or 'spinners', and yes, spinners are made for spinning! You can also find glass dildos more suited to anal stimulation.