The term formular (often misspelled formula) is an adjective applied to envelopes, cards and aerograms, etc., produced by postal authorities or to their specification, but bearing no imprinted or embossed stamp or other indication of prepayment of postage.
Formular stationery requires an adhesive stamp before posting.Van Gelder, Peter J.; The Collectors' Guide to Postal Stationery, A Squirrel Publication, Shrewsbury, UK (1997) Because they lack an indication of prepayment of postage or other related service, they do not technically meet the definition of "postal stationery", but the due to the similarities they are sometimes included in postal stationery collections.Is it postal stationery? Federation Internationale de Philatelie. Retrieved 12 May 2011.
Countries including New Zealand, Zimbabwe and Ireland have printed unstamped aerograms.
References
External links Formular Postal Stationery of Luxembourg