The rubber lines do swell, but only a little.
Folks remove old, damaged, failing rubber brake hoses, and replace them with new Teflon- (PTFE-) liner hoses with bright, shiny steel braid over the top. And they remark on how wonderful the new hoses are.
Well, yes, the Teflon-liner hoses ARE nice. But the biggest part of the difference was that the hoses removed were on the edge of failure. They'd have gotten a nice improvement in braking by simply replacing ancient rubber hoses with new rubber hoses.
Don't get me wrong...I've converted many of my vehicles to the Teflon-liner brake hoses. I've only installed a pair of rubber hoses (93 Lumina) in the last ten+ years--everything else has been Teflon.
My latest surprise was on my K1500, last fall. I had replaced the front hoses with Teflon-liner hoses during a major brake/suspension upgrade a couple of years ago; but I'd never bothered to do the rear hose. A broken bleeder screw in a rear wheel cylinder forced a wheel-cylinder change...which forced replacement of the brake tubing from the axle-end of the brake hose along the axle tubes. As long as I'm doing one tube to the right rear brake, I might as well do the tube to the left rear brake. As long as I've got the system open, and I have to bleed the thing, and both tubes are disconnected from the axle-end of the rear brake hose, I might as well disconnect the upper end, and replace the hose--since I've owned the replacement hose for two years already.
I put it all back together, and the brakes have never been better. The cynic in me says it was just the extensive brake-bleeding. More realistically, I think the old-but-OK-looking rear hose was starting to plug, restricting brake fluid to the wheel cylinders.