Look for silicone nipples. They are usually clear. Try the following link. I found the information below there.
Regards,
K.
http://www.tinyfootprints.org/forums/expecting-f/0003
Silicone nipples and pacifiers reduce the chance of latex allergies. Latex comes from the sap of the tropical rubber tree. Latex allergies can occur without warning and anyone can become allergic to latex. Children born with spina bifida, or those who have had many operations, have been recognized as having the greatest risk of being allergic to latex products.
Latex comes in different forms and is more likely to cause a reaction when contained in soft-poured products, such as gloves and nipples, than in hard products like car tires. The American Academy of Family Physicians has more information on latex allergies here http://familydoctor.org/254.xml.
Silicone, which is a synthetic rubber, does not appear to cause the same concerns. You can usually tell if something is silicone or latex because silicone tends to be clear and latex a yellow color.
Hope that helps!