Typically when you include respond cards with wedding invitations they consist of a card and pre-addressed return mailing envelope already having the return first class postage attached.
To save on costs, you may want to consider response postcards instead since return mailing envelopes are not required. Postcards can be mailed as is with the return address already printed directly on them. The postcard stamp for return mailing also costs less than a regular first class stamp.
Some wedding invitation designs may have the option of a matching response postcard design. Seal and send invitations actually have the printed postcard attached at the bottom of the invitation so guests can easily detach, fill out and mail back to you. If a matching option is not available, you can always order them printed on simple white or ecru cards as shown below.
Whether you choose to include respond cards or response postcards, the wording will be the same asking for the guests’ names and how many will or will not attend. A menu entree selection can also be requested if needed.