Here's how to fix up your Frogg Toggs to stop the melting. Works great, and does not require straps, etc like their heat shield. Do not try this on a rubberized or plastic suit. Nothing will stop them from melting, and this fix won't stick. This tip should work on other rainsuits made of similar fabric.
Buy a $3 ironing board cover and some Stitch Witchery for about another $3 (It is a heat sealing tape for hemming pants without sewing. Try a sewing or notions store, or the housewares section of your supermarket).
Cut one piece of the cover to line the inside of the leg from about mid-thigh down. Two pieces may be easier to work with. I suggest using pinking shears to get a zigzag edge that is softer than a straight one. Sit on the bike and be sure you cover areas touching both pipes when in riding position and when your feet are down.
Use the Stitch Witchery to attach the heat resistant patch to the inside of your Frog Toggs. Stitch Witchery is better than sewing because it does not make needle holes that will leak. Be sure you use a damp cloth over the material when ironing on the patch, as directed on the Stitch Witchery package. This protects the suit and keeps from getting the bottom of your iron sticky.
Then put on that suit, flip up the hood, put your helmet over it and ride in the rain. Not a drop will get to you and no nasty melted material.
[Gadget note: If you're following this tip because you've already melted some rain gear on your pipes, you might want to visit this Fixit page also.]
Thanks to Don Schaffer