Bigelow Tea
Long a mainstream supermarket brand, Bigelow now states plainly that all of its tea bags are biodegradable, compostable, and contain no plastic. The bag is wood pulp and abaca fibre. Roughly 90% of its bags are machine-folded with no adhesive at all; the remaining heat-seal lines are sealed with plant-based starches from corn and sugarcane rather than a thermoplastic. The paper is processed with oxygen and peroxide, no elemental chlorine, and independent testing (Mamavation) found non-detect fluorine on the bag.
The individual overwrap is a foil pouch (a light/moisture barrier), which is packaging, not steep-contact.
How clear are their specs?
A dedicated "are our tea bags plastic-free" page breaks bags into fold-sealed vs. plant-starch heat-seal vs. pyramid lines, names the bleaching process, and states no plastic - unusually specific for a mass-market brand.