The invention relates to a compensating balance-spring (1) for a thermally compensated balance and spring resonator, comprising a core (9a, 9b, 9c, 9d, 9e, 9f) formed from at least one non-metal material (11a, 11b, 13b, 15b, 11c, 17c, 19c, 11d, 13d, 15d, 17d, 19d, 11e, 13e, 15e, 17e, 19e, 11f, 21f). According to the invention, the core (9a, 9b, 9c, 9d, 9e, 9f) is entirely coated by a layer (7) that is stable in relation to humidity in order to render the compensating balance spring (1) less sensitive to climate changes. The invention relates to the field of timepieces.