Baby bottle nipples are manufactured out of Liquid Silicone Rubber (LSR).

 What makes LSR the material of choice for applications with such a high physical demand, is its high tear strength, which is normally in the range of 160 - 250 lb/in. Even emerging baby teeth cannot tear the nipples or bite off small pieces, eliminating the risk of swallowing particles or chunks of rubber. The tear strength of thermoset rubbers, thermoplastic elastomers and silicones can be measured according to American Society for Testing and Materials (ASTM) D624. It is defined as the strength required to initiate a tear in a material. This test provides a measure of resistance to tearing. Tear strength may also be used to illustrate the anisotropy of a material. http://thechemistrysideoftheforce.blogspot.com/ 

The ASTM D624 test describes the many different types of sample shapes that can be tested in a standard universal testing machine (tensile testing machine). Testing is performed by pulling specimens apart using the tensile test machine. The maximum force required to tear a test specimen is used to calculate the tear strength of the Die A, B and C specimens while the mean force is used for the T and CP specimens. 

Specimen	Name	Diagram	Grip Separation	Test
Die A	Nicked Crescent		500 mm/min (20 in/min)
Die B	Nicked Tab End		500 mm/min (20 in/min)
Die C	Right Angle		500 mm/min (20 in/min)
T	Trouser		50 mm/min (2 in/min)
CP	Constrained Path		50 mm/min (2 in/min)

[1] ASTM D 624: Standard Test Method for Tear Strength of Conventional Vulcanized Rubber and Thermoplastic Elastomers; ASTM International, 2007

[2] Campo, E.A.: Industrial Polymers; Hanser Gardner Publications, Cincinnati, 2007

To read more on why LSR is an excellent material for infant care applications from nipples, teething rings, toys and more, download our Liquid Silicone Rubber Materials and Properties technical paper. 

At SIMTEC Silicone Parts, a leading company in manufacturing high precision parts and components, we are exclusively focused and specialized in the production of LSR and LSR/Thermoplastic (Two-Shot) components.