A humectant is a substance whose moisture content changes very little even when the moisture content of its surroundings changes substantially. Humectancy is therefore different from hygroscopicity. A good humectant will for example prevent a cake from drying out when the cake is placed in a dry environment and conversely not make the cake ‘soggy’ when humidity increases.
Glucose syrups do not make particularly good humectants as their moisture contents change rapidly in response to humidity changes. The mid-range syrups, 43-65 DE, come closest to providing a humectant solution for a food manufacturer but sorbitol syrup is undoubtedly the optimum humectant for food and other uses.