It's really not a good idea to put them in the dryer.
DoIC posted this response:
"I've said this before and I'll say it again. This is not a good idea... You never know when a diaper is going to open up and lose its contents. They're not meant for that kind of abuse. That is not a mess you want to clean up, and it's a fire hazard, even without heat. I've encountered plenty of diapers that weren't well sealed. Also, the SAP crystals are small enough to work their way out through the weave of the top sheet. Ever noticed gel balls on your skin after wetting a diaper? That's because it doesn't all stay contained. Sure, some of it may be stray stuff that was just sitting on the surface, but...we're talking granules that are significantly smaller than a grain of sand when dry. They're rather difficult to effectively contain.
You don't want that stuff getting out and gumming up the workings of your dryer, or working its way into the heating system of the dryer. The gaskets on dryer drums are not meant to seal out particulates that small. Those gaskets are often made of fabric, too. Is suspect that dry SAP may also be abrasive enough to wear down those gaskets, as well. The edge of a diaper is also just thin enough that it could get entangled between the drum and the gasket, and nothing good will come of that. Heck, I've seen hair get into that spot and wreak havoc.
Sorry to go on a rant, but this is a safety issue. Not to mention, if you wreck your dryer, do you really want to have to explain to the repair person why there are shreds of a diaper entangled in it?"