Ok, first of all let me say I thought the right word was HYDROscopic, it's actually HYGROscopic. Check out this article:
http://www.theteacherscorner.net/lesson-plans/science/experiments/sbread.htm
I had a theory awhile ago about why my cakes placed in a plastic cake carrier behaved so strangely. Actually, I noticed that if I put a candy clay figure in the carrier with a cake that the figure would start to sweat. I also noticed that the frosting would droop and in some cakes even fall off my cake. And no, this isn't the 'no trans fat' issue because it's the same frosting I use on all my cakes, the only time this occurs is in those plastic carriers. Anyway, I did an experiment last fall. We were going on vacation, a 2 hour drive from our house (in cool weather), and I wanted to take some leftover cake with us. I put it all in the carrier, several pieces of cut-up cake and a buttercream rose that had dried out enough for me to handle.
By the time we got to our destination the rose and the frosting were soft and sticky while the cake had dried out a little. Here the sugar in the frosting had sucked the moisture out of the cake! Crazy right? But try it yourself, see what happens!
Anyway, just wanted to share this with you guys. I love knowing how things work, especially when it's something I have a deep relationship with....sugar!
Welcome to the wonderful world of understanding why food items do what they do! 
If you really want to be dazzled with all kinds of amazing food facts, pick up a copy of What Einstein Told His Cook: Kitchen Science Explained by Robert L. Wolke. Another fascinating read is On Food and Cooking by Harold McGee.
I want to get rid of mine too! I also bought those huge cupcake carriers that hold 36 cuppies, not a big deal when I just use bc but I made pharmacy cuppies last summer and my candy clay stuff was sweating 
I was so mad!
I had thought about drilling a few holes in the top of the carriers to see if that helps but I wouldn't want to compromise the handle. Any thoughts on that one?
Thats why they reckon using glucose when making candy keeps it harder for longer
Or using isomalt for sugar sculpture is best because it attracts less moisture!
It's to do with the amount of moister different sugars can attract
Using glucose in your fondant can improve this.
Ever have your sugar syrup crystalize? Bet you made it with regular sugar? Try glucose!
What if you just did a couple on top and a couple randomly on the sides. You wouldn't want to weaken the structure too much. So you would vary the heights of the holes. Not sure it would work but might be worth a try before tossing them.
Just a thought.
Judi
Wait wait I know one--about the sugar re-crystalizing. If you drop a tad of any other sweetener, like a drop of honey, agave, corn syrup or yes glucose in there the sugar crystals will be foiled and this will prevent re-crystalization.
I make a toffee filling and I freak out equally about overcooking and it turning into a sweet sand castle or under cooking it and it won't set up. So this way I can over cook it to my heart's content and add the drop of honey and I'm golden.
Very interesting. What about the cakes in a supermarket, which are packaged in plastic containers and, left on the shelf for 5 days. Or leftover cake at home. I always cover it with plastic wrap and if I don't it gets dry quickly. Maybe I don't put enough sugar in mine. Or maybe the air in California is dryer.
I am going to have to think on this one some more. Maybe I need to go bake a cake and do the test.....and eat the slices which don't make a nice square.
BCjean sounds like you have good icing to me at least you can stop yours from going hard with some wrap.
But to help (I won't say stop, not that knowledgable yet) it from going soft could mean having to adapt a recipe and I hate having to go through all that but it's a neccessary task sometimes.
You can try adding a little tylose to your fondant but that's a fine line as far as the taste and texture buds go!
See scratch fondant uses or you can use glucose in it's making which attracts less water than regular sugar so would suggest that this is a better fondant when it comes to the moisture stakes!
Cream of tarter acts like honey as k8memphis mentioned. It interfers with the sugar so maybe adding tarter to the MMF may help combat the issue but I have not tried this yet and it would help cut the sweetnes of the mmf too but I don't know what other effects it may or may not have.
Just something I have been thinking of trying!
I regularly store cakes and cupcakes in my cake keepers of various brands - Sterilite, Wilton, Tupperware, etc., and have never had the cake or icing change in quality at all.
If it were me, I would definitely drill a few small holes in the lid of one carrier to see if it made a difference.
Thank you for the suggestions, I definitely think the staggered holes should work and what I have I got to lose? They're just gathering dust!
banba-it's candy clay, a mixture of chocolate and corn syrup, not fondant. I could alter the mix some but that would mess with it's workability.
BCJean, I bet you're right, I live in a highly humid area, well, in the summer time anyway.
Hmmmm, I like the honey idea, this is gonna be a fun year of experiments 
I live in a humid area also, and noticed this, too. Just glad to hear that I am not crazy!
another good bakign book (why/how of baking) is called Bakewise by Shirley Corriher..It has recipes but I enjoy the reading..
yep.. it has a bunch of useful information (unuseful to some LOL) baking soda is about 4x more powerful than baking powder.. It also says the amount (i dont have it with me right now) of soda it takes to leaven a cup of ap flour.. good stuff!
Another good idea would be to put some dry crackers (saltines, for example) in with the cake or cupcakes (maybe even taped to the inside of the lid with enough of the cracker still exposed?). The issue is that all material strives for homeostasis, or the most stable physical state of equality. If you start out with perfectly dry fondant over perfectly moist cake, and you enclose it in a little micro-cosmos like the plastic cake carrier (which insulates it all from the relatively drier air outside), everything inside that cake carrier is going to try to equilibrate, and the cake will lose moisture and the fondant will absorb it. If you include some crackers, you could conceivably have the dry crackers absorb some of that moisture from the air in that micro-cosmos before the fondant does. It works well if you put crackers in a sugar or salt shaker as well, to keep the sugar/salt from clumping on a humid day.
Hello everyone,
I'm living in Beirut(lebanon) where we have a high humidity and everything is sweating especially on the summer days.I'm trying to get in business as cakedecorator and then I faced this problem-what can I do if my cakes will sweating?Then I thought that I could put some of those little bags of silicagel(we find them on the shoes when we buy it 
) arround my cakes?Oh,I guess it's a crazy idea?
I made a research and I found that is proper for foodstuffs.
http://www.propackvci.com/en/action-productos.prod+id_prod-17/packaging/Antihumidity/Desiccant+bags/Propagel+desiccant+bags.html?gclid=CP7y95vRtZgCFQrAGgodMgppbA
What do you think?Is it a good idea?If yes,where can we find this silicagel (except the new bought shoes )
Oh sorry seriouscakes I thought you were talking about the fondant on cakes too not just the candy clay
You could try finding out about making it with a different syrup other than cornsyrup mayb that would help it a little, not sure? Chocolate will sweat anyway as it's melting but I am sure there must be someway of making it a little more stable and still keep it's workability factor.
Chocolate sugar paste uses the same ingredients as candy clay with the addition of some sugar paste added to the mix maybe you could try that? As the sugar paste would contain glucose I am thinking that would aid the candy clay a little?
Ortansa that's a good idea with the food safe silicon gel for packaging, would work like the biscuit or cracker emiyeric mentioned.
Shirley gave me a link to a product on creative cutters. maybe its similar to what ya'll are talking about
http://www.creativecutters.com/index.php?option=com_simpleshop&Itemid=42&task=viewprod&id=1716
So THAT's why when I transport cuppies in my plastic carrier they seem a bit wonky.
I feel like this thread should be a public service announcement.
*Rainbow*
The More You Know...
lol, maybe I'll start up another post with that in the title and direct people here
Hmmm, I live in Virgina and maybe the humidity isn't as bad here as what some of you experience where you live. I absolutely love the carriers. Matter of fact I have like five of them and I always decorate my cakes the night before I need them and place them in the carrier. The cakes stay so fresh in them and I have never had the problem with the cake sweating. I've used the carboard boxes but my take on them was that it made the cake appear stale pretty quickly. Funny how we have different experiences.
Wait, the cake *itself* isn't sweating, it's the candy clay figures. The frosting does get softer and more sticky though and on occasion has completely slid off the side. The only time THAT happens is in the carriers though....
I regularly store cakes and cupcakes in my cake keepers of various brands - Sterilite, Wilton, Tupperware, etc., and have never had the cake or icing change in quality at all.
Same here. I've been using plastic boxes for cakes since I began doing cakes 20 years ago. My clients pick up the cake in the box and return it when the cake is gone, usually within a few days. They love the boxes because the cake stays moist till the last piece. I have never had icing slide off a cake. I don't use candy clay or fondant, so I don't have an answer about that.
I love using the plastic boxes because it's easier for me to be "green"...I don't use anything disposable except the foil on my wooden boards, and the foil is recyclable. My clients like that aspect as well. Everything is easy care and washable.
Alright, here's the sequence of events: cakes baked and frosted Monday, left uncovered at room temp until Weds., placed in plastic carrier for transporting, then removed about 1 hour later. Seriously, they only spent an hour in the carrier! You can see from the before pics that they were FINE, no bubbles, nothing.
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