Now that we've started to approve our formulas for production, we'll be using these tubes for "stability testing", a mandatory 90-day test our labs run on each formula to make sure it holds up over time and doesn't react adversely with the packaging material we plan to use (in this case, mono-layer medium-density polyethylene (MDPE) with 50% post-consumer recycled waste (PCR) - what a mouthful!).
Basically, the lab fills 50 tubes with the formula in question, stores them into an insulated room, turns up the heat, and tests a handful of tubes every few weeks to see how they're holding up under duress. If, after 90 days, a product comes out the other end intact, it's deemed stable and ready for production. 90 days under heat is meant to replicate a 2-3 year shelf-life.
Natural products are inherently less stable/more volatile than their chemical/conventional counterparts because they aren't packed with bomb-proof chemical preservatives. That said, the best formulators are figuring out how to use natural (plant-derived) preservative systems with good results. In some cases, small doses of inert/safe chemicals are necessary.
Obviously, we're hoping we get the green light on all of our products so we can move straight into production.
