This experimental research reports the development of mortars with enhanced potential to passively adjust the relative humidity of interior building envelopes, achievable by introducing porogene additives—aluminium powder (AP) and sodium olefine-sulphonate (SOS) and superabsorbent polymer (SAP). Samples with 0–0.10 wt% AP, 0–0.05 wt% SOS, 0–0.50 wt% SAP and water/solid weight ratio nearly constant (~21%) were produced to estimate the individual performance and optimal dosage of mentioned additives. SAP dosage was limited to 0.5 wt%, since it assures the good compromise between the maintenance of the common properties (namely the mechanical strength) and the moisture buffer capacity. Samples containing 0.050AP and 0.025SOS showed the optimal performance. Moisture buffer capacity of all samples was classed at least as good, upon determinations obtained by following the Nordtest protocol.