Yumbox
Yumbox's signature product is plastic. The Original and Tapas boxes use a molded plastic tray and a plastic lid whose leakproofing comes from a silicone-lined seal, marketed on "BPA-free / phthalate-free" rather than on being plastic-free. Food sits in the plastic tray for hours, often packed warm. Yumbox's stainless steel "Pret" line moves the tray to steel but still relies on plastic and silicone components - a step up, not plastic-free.
How clear are their specs?
States that the boxes are BPA- and phthalate-free and that the seal is silicone, but does not publish the specific plastic resin used for the tray and lid.
Products to avoid
Documented so you know what to skip — each still has a full breakdown and sources.
