Mu brothers 2012 f250 had stock body bushings made of foam. They failed and broke to pieces when the truck was only 10 years old.
Made for a soft and quiet ride until they failed, LOL.
SO I guess there is good and bad to softer.
Now for a little body mount rant...
Late model stuff mostly. But I have seen vintage stuff show the same to a bit as well.
Bodies are stiffer than the frame. I've pulled a body mount bolt at the core support while a truck is on the hoist and watched the frame flex down and leave 1/8" gap. The body mount was holding the frame in place. Bodies are pretty stiff. All that crash protection. Doors that people want to still open and close. The frames are noodles. The half ton stuff is floppy. The 1-ton stuff gets a lot stiffer (hey that's one of the reasons they tow so much better).
The cab mounts on trucks, especially the last set at the back of the cab, take a beating. You need something to hold the cab up off the frame. They have to be fairly rigid. But they also have to give enough that the frame flex won't tear up the body. There gets to be a lot of engineering to design them to do that. And that is before they even get into the isolation of the body from the frame.
But they can't just be giant jello blobs. Need to keep a fairly tight tolerence of body to frame. Bumper gaps on late model trucks get tight to help fuel economy (yes that really is a thing). The gap from cab to bed, tighter the better, but not so tight that the cab and bed hit when flexing. what you call foam body mounts, are probably actually microcellular. They have been using those for suspension bumpstops for decades now. A vast improvment in ride quality over rubber ones. Sort of a poor mans air bump. I never knew they used them in body mounts, but I could see them being used there. I have converted a few late model vehicles that had factory rubber bump stops to microcellular and the bottoming performance is day and night improved. It can go from a solid bottoming out to lightly bottoming out and not even noticing. You can still feel it when you hit really hard.
Looking at the silicone body mounts. It looks like the silicone material I have for a work surface. Very rubbery like. I suspect you won't tell much of a difference between the silicone and fresh rubber. But I suspect the silicone will have less aging compared to the rubber.
Little side note on silicone vs. rubber, silicone stuff tends to propagate tears worse than rubber. Rubber can have a little tear and it takes more force to continue the tear as compared to silicone. The silicone tends to have more stretch without issues and doesn't age like the rubber. But when it goes, it goes. I have some silicone stuff for scuba and can compare it to direct replacement parts of rubber. Probably not the fairest comparison, but the only direct one I have.
