That material is Phenolic or G11 Garolite. Both have excellent thermal heat resistance used for heat insulation. I’ve used it (Phenolic ) many times in carbureted and fuel injected applications to insulate the carb or FI manifold from heat. I’ve never used it in a thickness less than 3/8 or in a rotary application.
I will use it between the LIM and UIM, that will help heat reduction.

 

I didn't know Phenolic was the material, but that's what mine is, made by Gizzmo. I'm not sure how well it would hold up but I'm looking into getting spacers made anyway, using the OEM gasket as a template, and using aluminum I suppose. Et3rNaL (he needs one too for the same reason) and I went to a waterjet place this afternoon to look into getting them made. We're going to test them and if they work alright with no issues we'll have more made and they will be available to whoever needs or wants them. Since they will be aluminum, they will not have thermal barrier characteristics, they will be offered as merely a spacer.

 

What's the purpose of this spacer exactly?

 

For me it's to space my fuel rails apart since they were pressing against each other with the regular gasket on there.

 

I have one in my car, no problems so far. I also have an extra one if anyone wants to take it...