Media Bottles are manufactured from borosilicate glass that conforms to USP Type I requirements and has a low alkali content to help prevent changes in pH to maintain the purity of its contents. There are two types of media bottles offered: Media bottles with a 33mm neck size (38 mm for the 1 Liter size) or 45mm neck size. Both are available with or without the caps attached. In addition, there are a variety of liners for the black phenolic caps available including rubber, PTFE faced rubber or low density polyethylene. The 33mm neck size 1 Liter bottle features hand grips making handling easier.