Is the heat source on the top of the incubator? What I'm getting at is that if the heat source is not, then the top of the incubator isn't likely to get any hotter than the rest of the incubator. There are plenty of foam incubators and they don't melt. But, if you have an intense heat source (60W bulb or higher), and if the styrofoam gets too close to it, then the styrofoam will melt.
Yes, the lamp is touching the styrofoam. The bulb itself is not. The bulb is a 60W. Maybe I should switch the bulb to a 40W? Or trim the styrofoam? Here is a picture of my bator. (Sorry about the quality of the photo.)
If the cowl of the lamp is hot to the touch, I'd either get a lower watt bulb in there or find a way to break the contact between the metal and the styrofoam. Polystyrene (styrofoam) will start to deform at 90 C (194 F, near the boiling temp of water).
I trimmed the styrofoam so that it is no longer touching the lamp. I also added tin foil around the inside of the foam (between the foam and the lamp) which is also not touching the lamp. Now I just have to raise my humidity.