Compressionless Brake Housing
 

Anyone been using this housing for some time on a rear rim brakes?

Supposedly nicer, but am nervous because it used to be a no-no for brake housing.

Quite common these days. Our Supremo knows no different as a matter of fact today I’m changing out the brake cables for the first time since the bike was new.

So why was it a no no

Maybe it's a no-no to use shift cable housing directly? Compressionless brake cable housing (other than the solid aluminum links sort pioneered by Nokon) is basically shift cable housing (linear steel strands) plus some reinforcement. For Jagwire KEB-SL that reinforcement is kevlar. For Yokozuna Reaction housing, it's an extra layer of the traditional steel spiral housing. Without the reinforcement, I suppose the housing might burst causing a brake failure. So that would be the no-no.

Anyway, I've used both Jagwire and Yokozuna without issue. I think the later performs better, but might be larger diameter, so might not fit in any existing cable guides. I always use full housing, so don't use cable stops. I use Shimano cable grease for the inner cables as well. The housing isn't very flexible, but you still have to zip tie it or otherwise connect it to the frame using something like a clamp on cable guide every short distance because you can lose performance due to the cable flexing when the brakes are applied as well.

Normal spiral housing, properly routed, IS "compressionless".

The difference in feel is likely due to the stiffness of the housing - not all cables are routed in simple curves, and in such places a stiffer housing will deform less.

Shift housing - still a no no for brakes. It WILL fail.

Compressionless brake housing - works great, different from shifter housing in that there is an extra layer of Kevlar or steel wrap keeping it from bursting open under braking force. Make sure to use the proper ferrules too.

yes, this is exactly it. Shift housing has nothing but the flexible plastic layer holding it together and under the stress of braking, it will not hold together

I've used both Yokozuna and Jagwire compressionless housing on different bikes. I found that yokozuna had slightly less compression than jagwire but it's more difficult to work with since it's a larger diameter than normal housing requiring special ferrules and is more work to cut also. The ferrules and housing design also don't seal up quite as nicely as the Jagwire setup.
There is inherently some compression in spiral housing no matter how it is routed, that is why it isn't used in shifting (with indexing especially there is just enough compression that it won't work correctly). Truthfully unless you are trying to get every bit of performance out of your setup it's not a huge difference though. The switch on my mountain bike from cable discs to hydros was much bigger than standard housing to compressionless swap for example.

It's not compression - there is metal-to-metal contact from coil to coil all along the housing.
(I supposed this is technically not true, as each coil is pressed against its neighbour there is some elastic flattening at the contact points due to the low degree of osculation, but this is small relative to the total length.)
It's flexion - the inner cable is smaller than the outer, and if you have a compound curve the housing will tend to straighten slightly during braking, taking up the clearance.
"Compressionless", as most have noted, is stiffer than coiled housing, so it feels different.

It's pretty easy to see this with coild housing on the run from a non-aero rear brake lever to a rear brake.
If the front section is not the correct length, when braking it will flop about beteen the lever and the first top-tube attachment of course, but even when correct you can see the housing change a small amount.