Glass shelves come in ¼, 3/8 and ½” thick.  Regular or Tempered (5 times stronger).  We offer regular clear (green edge) or “low iron” glass which is more like a crystal type glass. Ask our sales staff what thickness we recommend for your intended size, weight and use requirements. Glass tops are typically made of ¼” annealed glass.  While tempered is stronger, if it does break, it shatters and may damage your table.