Silicon is less than ideal for more than one reason, not the least of which is the issue with benzyl benzoate incompatibility. BB will cause a breakdown of the silicon, and cause it to leach into the oil, which isn't necessarily a visibly detectable process, but introduces contaminants nevertheless. In my opinion, silicon is a no go for AAS. A source on here couldn't get their normal stoppers and used silicon very briefly. Unluckily, I got a bunch of them in several orders I placed. I said something about my bad luck, and they reached out to me and replaced all 32 vials I had received that had silicon stoppers. They promised Meso to never use silicon stoppers again. Another source has also switched from silicon to PTFE and Flurotec, and while they noted they will need to charge $1.50-$2.00 more per vial(these coated stoppers are significantly more expensive than plain butyl or chlorobutyl stoppers), every single response was unanimously in support of the switch and increased price. Anything I buy that uses silicon gets re-vialed, unless I plan to use it in a short period of time.