We guarantee shelf life of one year as a commercial matter, but 2 - 5 years in not uncommon.We've even seen cases of 10 years and in one case 30 years.
It all depends on exposure to heat over time. If you want to extend the shelf life of the rubber, store it in a refrigerator (but NOT in the freezer).
Rubber does not go bad suddenly but ages a bit everyday. So it can be old and still usable for a long time.
Thank you for using Castaldo products and I hope this answers your question!