I don't know about folding them it seems like they would separate after maybe 50 uses or less, With cards like that they really ought to use some other type of material besides paper
Nah, I think it was Vangelus who did a test and they stand up if you fold them. You have to really pull them or bend them the wrong way for them to break. if you are worried, take a common one and just fold and u fold it for a while while doing something and see your result
I'll tell you this, I've been playing, and I play A LOT, and I fold all my characters, nothing has been happening, not even any fraying at the corners. But you also don't have to fold them. Just use a marker to identify which side you are.
Yeah the cards have been stress tested, there's a video on YouTube where one of the members here took a copy he found in a blind pack and used it to stress test, folded that thing like 100 times, flopped it around really fast, ect. nothing happened. And they aren't just paper by the way. It's a pretty hefty piece of card that's been laminated to give it some extra strength. The cards even feel a bit more sturdy than the ones that don't fold in half. The only problem is whatever they do to these things that makes them so sturdy also some times makes them a little TOO sturdy. Like some cards won't even fold all the way. Some of them seem to fold instantly without even trying while others can pretty much stay solid until I decide to fold them. QC issues aside, I've yet to see or hear of a card ever ripping in half along the fold. The most damage I've seen is a small crease line on the "solid" side of the card. Cause they only fold in one direction, one side always has a crease where that hinge is while the other side looks solid until you fold it a few times. It also tends to be the foil side of the card and I think it's that foiling that's cracking when the card folds not the card itself. Anyway... unless you're running something sharp along the fold or pulling the two halves in opposite directions specifically trying to rip it in half I don't think you really need to worry. But if you don't like seeing the small crease line across the foil then you might not want to fold them at all. That's really the only way to avoid that. It doesn't really bother me since there are going to be cracks anyway, that's just the nature of Combiner cards so a few extra fold lines aren't even that noticeable among the other lines between each card that makes the combiner. Might bother me more on triple changers but I don't have any of them...
The only time I've seen a card "break" was when someone purposefully bent it in the wrong direction and kept applying force until it popped. Wizards stated that they tested it to "a few hundred folds" with no damage before approving the three sided cards.