Hevea Baby Glass Bottles are made from 100% borosilicate glass, which is both heat and thermal shock resistant. Glass is the safest alternative to plastic as it does not leach any toxic chemicals, it is taste and odour free and is more hygienic as its smooth, non-porous surface is easier to keep clean. The anti-colic, medium flow (3-24 months), 100% natural rubber nipples are BPA-free, phthalate-free and PVC free, softer than silicone and very resistant to teething/bites. Additional natural rubber nipples of slow flow and medium flow can be bought separately. Hevea's glass bottles are standard neck bottles which mean they are compatible with most standard size breast pumps.