I have a 2-layer G-Force race suit (nomex) that I'd like to add a couple small patches from my sponsor to. I've done a lot of searching and there seem to be a million answers about "how to" or "whether to".....some say to only stitch through the upper layer, but not the nomex layer. Others say to use Nomex thread and stitch through both, or just one. Other say to use cotton thread so the patch "falls off" if you're on fire.
Looking at my GForce suit (brand new, SFI 3-2A/5), I noticed that the SFI patch on the arm is actually sewn on through both layers (outer and nomex layer) with the stitching visible on the inside, so that would kind of indicate that's the way to go (using Nomex thread, I assume).
So, thoughts on this? The suit will be used initially for Lemons and Chump, but would like to make sure I don't make it "out of spec" for other types of racing should time and budget allow them in the future (e.g. Rally America, etc).
Mine are sewn through with nomex thread. I bought it 2nd hand from Wally Dallenbach Jr's team so... that's how the pros do it.
IMO, if the patch isn't nomex or proban, you want it off the suit as soon as possible. But I'm just paranoid that way. 
Glad this was posted. Just got a new suit today and was wondering how to put the required NASA patches on.
Where to get nomex thread?
Showing my noobness regarding firesuits, how do you sew through only the outer layer? I thought multilayer suits were still essentially "one piece" or no?
Pegasus has nomex thread.
https://www.pegasusautoracing.com/productselection.asp?Product=2131
I deal with a lot of Nomex / fire situations. If it gets to the point where the thread on your patches is starting to burn up, you have bigger issues to concern yourself with.
I agree with Woody (firefighter?). Most synthetics will melt around 250c and at that point things are going to get worse before they get better. My gut feel would also be to use a meltable thread if the patch isnt flame resistant/retardant to get it off, but if you are in a car where can it go other than your lap!
You can use Nomex or Kevlar threads, the latter might be easier to find. To go through just the top layer you probably would have to hand stitch it.
Depending on your locale, you might ask a local embroidery place that serves the local dirt track/stock/sprint car clientele...
