A gasket makes the seal. Material choice follows the product, the temperature and how long it sits: what suits a water-based food product may not suit a solvent. Gaskets are usually part of the closure specification rather than an afterthought.
Where you meet this term
If this becomes a real requirement
CAQUIN sources industrial packaging to specification. Send what you use today, roughly how much, and where it ships — a photo is enough to start.