You may be wondering what makes a formal wedding invitation formal. Typically a formal wedding invitation is created on a nice piece of white paper and has type that is black. The body type is usually all caps, typically the use of small caps is preferred, and the names of the newly weds are in a script font. Sometimes there is use of embossing on the paper. Formal wedding invitations also typically have a piece of tissue paper over the invitation.
Formal wedding invites almost always have inner and outer envelopes. These are used to help protect the inner envelope and make it easier to address them to people because there is more space. More than anything it does make the invitations more formal. Using the envelopes that have a pointed flap rather than a flat flap on the back also adds to the formality of the invitations.
Another thing that creates formality is in addressing formal wedding invitations. I go into more detail of this in my article about envelopes. This is something that should most likely be done whether you consider your invitation very formal or not, unless you are trying to create a very casual and fun atmosphere for your wedding. Wording for formal wedding invitations is another thing that can lend itself to creating that since of formality.
One of the most important things to consider when creating a formal wedding invitation, is what does the style communicate to your guests. Do you want the event to be a formal black tie event or do you simply like that style of wedding invitation. If it is the latter, then you should definitely address the dress code inside of the invitation. If you want it to be a black tie event, then it may still be a good idea to address this in the invitation.
In the past the things told people that the wedding was a formal event. Today, things seem to be a bit more ambiguous with people not really always being sure of the rules. If you have something in mind, it may be best to simply let your guests know. Of course it is not required to have this type of wedding invitation if a formal event is desired. There are many ways to create beautiful formal looking wedding invitations without following these conventions.
I'm a graphic designer who has been working in the field for 7 years. I have recently graduated from the University of Houston. I have created many invitations for friends over the years including some wedding invitations. I really enjoy designing them, and am working on being able to supply them sometime in the future.