The Hubble Radius is one of those things about the standard cosmology that's commonly missunderstood. The distance keeps growing. So pages like the following are incorrect.
The Universe Adventure - Hubble Distance
(If that doesn't work, try this.)
The Hubble Radius
You might read that the Hubble Radius is what we can see, like it's another way of saying the visible universe. But that's not right. The Hubble Radius is the distance at which the expansion of the universe adds up to the speed of light. An important part of the standard cosmology is: the farther galaxies are away from us the faster they move away from us. It's not acurite but it's pretty consistant on average. A galaxy twice as far moves away twice as fast. So if you go really far, far enough, galaxies must move away at the speed of light. That distance is the Hubble Radius. It surounds us like a bubble. Anything outside of it moves away even faster than the speed of light. To be clear, cosmologists don't like to say "move" since that implies those things are actually moving through their space. And nothing can go faster than light. It's really the space between us is expanding. So instead, they say "recede". So at some point, galaxies must reciede away from us at the speed of light.
The Expanding Radius
The interesting part about the Hubble Radius is that the light beyond that distance can't get closer to us. The space between us is expanding too fast for the light to get any closer. You might think it reasonable to conclude that we can't see anything beyond that hoizon. And this is where the trouble starts. If the radius stayed the same size, that would be true. But it's expanding with the universe. It use to be a lot smaller back when the universe expanded faster. The size of the radius is closely tied the the age of the universe. The radius now is about 14 billion light years. That's close to the age of the universe. And when the universe was younger, the radius was smaller.
Seeing Beyond the Radius
We can see galaxies that are outside the the Hubble Radius and have always been outside. Few galaxies cross from inside to outside the radius (or vice-versa). Any galaxy with a redshift Z of 2 or more is outside the radius and has been outside since the light we see left that galaxy.