Chai (חַי) is the Hebrew word meaning 'life' or 'living'. The two Hebrew letters that compose it — chet (ח, value 8) and yod (י, value 10) — have a combined gematria value of 18. As a result, the number 18 carries profound significance in Jewish tradition, and gifts in multiples of 18 (18, 36, 54, 72, 108, 180, 360, 1,800) are a customary expression of the giver's wish for the recipient's life and wellbeing.
Tannenblut's Double-Chai Vessel tier (priced at € 324) is named for the multiplicative form 18 × 18 = 324, an intensification of the Chai blessing into a square form. The numeral 18 itself appears in the Holy Numbers Edition, accompanied by a Hebrew document referencing the Tanya.