edit: If no air exchange, it dries slower, inviting mold. There is such a thing like an ideal "drying to age" ratio to keep age-related staleness at a minimum

edit: If no air exchange, it dries slower, inviting mold. There is such a thing like an ideal "drying to age" ratio to keep age-related staleness at a minimum w/o having to care for mold. What I mean is, older bread should be drier than fresh bread, not too much, not too little. Correctly kept, it dries out (only after several days) instead of getting moldy. About your situation: I've to admit that I don't know about keeping bread well in such bad conditions. I'd try a slightly more sealed container, or if that doesn't work, slice and freeze it fresh. Other than that, find uses for dry bread (works perfectly fine in soup, or if white bread, make breadcrumbs etc. etc.). 20% rel. humidity is so low that it is very uncomfortable for humans, even unhealthy for some people. Are you really sure that's your in-house humidity? Outside/inside are often very different, due washed clothes drying, cooking, plants, respiration, and also humidity from the cellars in some buildings. If yes, and if possible, I'd recommend an air humidifier to get that up to 40% or so. Depending on volume, a $60 unit should be able to do this, even if it will take three weeks until the humidity slowly approaches sensible levels.