Glass sex toys are commonly made from clear medical grade borosilicate glass ("hard glass") of which Pyrex is a brand. This material (essentially "lead-free crystal") is completely non-toxic and will withstand extreme temperatures as well as physical shock without compromising its structural integrity. Glass toys made of borosilicate are completely safe. A properly annealed inch thick piece will withstand up to 3,000 lbs of pressure and extreme heat and cold. Glass dildos are also non-porous and can be sterilized to help prevent infection with reuse. These types of sex toys are not only durable, but also visually appealing, often considered by some to resemble works of art. Glass sex toys are a long lasting alternative to less expensive toys. The toy can be heated or chilled before use. Some higher end glass dildos feature Swarovski crystals. Other toys are covered in 24-carat gold.