Mason Bottle
The whole product is a plastic-avoidance strategy: take a glass mason jar and add only stainless bands and silicone nipples, spouts, and straw tops, so liquid never touches anything but glass, steel, or silicone. That earns a "silicone-only" rather than fully plastic-free rating, since the parts a baby's mouth and the milk contact are silicone - but silicone in the nipple role is genuinely hard to replace, and there's no hidden plastic liner the way conventional bottles have.
How clear are their specs?
Plainly lists the only three materials in the liquid path - glass, steel, silicone - and builds the pitch around that constraint, so there's little left undisclosed.
