Measuring 5.5" X 8.0", the accompanying envelope is marked "Extra Postage Required", but I'm certain it's not for the size. My guess is that it's for the weight.
That card is printed on the same durable bond stock as many other cards, but the interior has some minor 3-D 'pop-up' effect and a prerecorded sound chip (which now no longer works).
As you can see in the upper right hand corner, the activator is hidden under the words "Press Here". Less obvious from this picture, but easily noticed when holding it, is that the sound-making device and speakers are hidden under Batman's torso.
The sound chip plays the theme to the TV series, credited to Andy Sturmer on the back of the card. Frankly, of all the audio clips a little kid could drive his parents crazy with by repeatedly pressing that button, this is definitely one of the better ones. I wish now that I had pulled this card out a few times over the years for a cheap little pick-me-up before the battery died. Instead I tucked it out of the way and kept it clean, then forgot about it until I stumbled across it last week.
For however many years Hallmark had permission to use this iteration of Batman, they made full use of it, covering every commercial aspect of a child's birthday party. They used different poses of him and different backgrounds for invitations, plastic cups, tablecloths, etc. And they've used many more iterations of Batman for their Christmas ornaments.