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Octane Universal Material - Guide + Starter File
Octane introduced the highly versatile Universal Material in 2018. It's great for integrating Substance files and other material map sets, but even better than that, it replaces the need for just about every other type of material type in Octane. Once you learn what all the channels do (and you will if you keep reading), it vastly simplifies the whole material making process. You can grab the scene file here that contains the Jedi Training Shaderball that I modeled (which is UV mapped kindasorta well), and all the materials in this document. Everything is CC0, so use it however you want.
Above are the five basic types of material you can make with the Universal Material, and how to build each one. These are achieved by messing with only 5 of the 22 different sections in the material. The rest of the sections layer on effects on top.

When you're first getting started, the most important thing to remember is that a new default Universal Material starts off with the Metallic channel set to 1. This completely overrides the Specular channel, so until you reduce that, all your materials will look like metal and you won't be able to get a matte, plastic, or glass material.

The second most important thing is the Float value found in many of the channels. Float goes from 0 to 1, and refers to how much contribution the channel has to the overall material. Color always overrides Float, so if the Color is set to anything other than black, the Float does nothing. The potentially frustrating part is that if the color is set to black, the Float will override that, so it's possible that you'll be expecting your material to be black, but the material looks gray or white- just remember to check the Float if this starts happening. When you're making a black material, sometimes you need just the smallest bit of contribution to the channel to kind of wake it up (see Metallic channel below), so Float is handy here for setting extremely low values like 0.01 or 0.001.

With that out of the way, let's explore all the various channels...
Octane Universal Material // Albedo Channel
The Albedo channel (referred to a lot as Diffuse in other apps and even other places in Octane) is the overall color of the material. With no Specular, Metallic or Transmission contribution, this produces a matte material. The default Universal Material has the floats in both the Metallic and Specular channels set to 1. To get a matte material, just bring both of those to zero and make sure the Specular color is black.

Substance map: Albedo, Basecolor, or Diffuse
Octane Universal Material // Specular Channel
The Specular channel creates a glossy finish on top of the Albedo color. The Specular color affects both the intensity and color of the reflections. By default, the Universal Material has the Metallic channel set to 1. To get a glossy plastic, set that to zero, give the Albedo channel a color and give the Specular channel a color.
Substance map: Specular
Octane Universal Material // Metallic Channel
The Metallic channel makes a material more or less, well, metallic. The complex properties of a metal material are controlled in the IOR Channel (see below). For an easy metal, just leave the Metallic float at 1(default for a new Universal Material), and set the Albedo to whatever color you want. You can also drag the Metallic float down to make a semi-metallic looking material, and then the Specular channel starts to affect the material again. When making a black metal, adding just the tiniest bit of Albedo in the mix can change the look pretty drastically - this is where you'd make the color black, and use Float with a small value like 0.1 or even 0.01.
Substance map: Metallic
Octane Universal Material // Roughness Channel
The Roughness channel makes the material more or less rough. This effect is seen in reflective materials such as the metal on the left of the image above, or refractive materials such as the glass on the right. A little roughness goes a long way. The visual difference between low float values is much greater than higher float values, so always start really low (even 0.01 or 0.001) and work up incrementally. Roughness can seriously beat on the GPU if you're using it with certain types of glass (or Transmissive) materials, so if your render times start going crazy, see if this is the culprit.
Substance map: Roughness, or inverted Gloss
Octane Universal Material // Anisotropy Channel
The Anisotropy channel produces a special kind of reflective effect that mimics the surface of certain metals, plastics, wood, hair, and concrete. It works really well on metal, but also works on specular type materials (glass, shiny plastic, etc). The setup can get pretty frustrating since there are four steps needed to get this to work. if you miss any, it just won't and you'll be flinging sliders around and yelling at the monitor (definitely not from personal experience.) 

1. The material's BRDF type (Basic tab of the material) must be set to GGX or Beckmann - not Octane, which is the default. 
2. The Anisotropy slider in the Anisotropy channel needs to be set to a non-zero value (usually 1). It can be set to a negative value too - worth exploring. 
3. Something in the Roughness is needed, either by giving it a value like 0.5 (good place to start), or by using a grayscale texture. 
4. Finally, a grayscale texture (image or procedural - it's not picky) needs to be used into the Rotation section of the Anisotropy channel (it has its own node if you're using that view).

The above image shows what happens when you connect the same map (shown in the first shader ball) into the channels noted below each shader ball. Putting it into both the bump and roughness channels gives a fairly similar effect, but the light won't distribute like a true anisotropic surface when the object turns. Putting the map in both the Roughness channel and Rotation input seemed to yield the best result in this example.
Substance map: Anisotropy and/or Rotation
Octane Universal Material // Sheen Channel
The Sheen channel produces a satin-type finish to the material. In the image above, the Albedo has a dark gray color, and both Specular and Metallic have been brought to zero, so the soft glow on the edges is just coming from Sheen. This can be added to metallic or specular type materials as well, but is most visible in a matte material like cloth. The sheen Roughness slider affects how spread out the effect is. A bump or normal map can also be added to the sheen to break it up.
Substance map: Sheen, Sheen Roughness, Sheen Bump, Sheen Normal
Octane Universal Material // Coating Channel
The Coating channel puts a glossy layer over the top of the material. It can be put over any type of base material and creates some interesting effects as can be seen in the image above. Coating has a few options - Amount (float), Roughness, and IOR. The first two are pretty self-explanatory. The IOR controls the look of the reflections. 8 is super shiny like chrome. 1.5 is similar to glass. The coating can also greatly enhance other effects like the Thin Film layer.
Substance map: Coating or Clear Coat, Coating Roughness, Coating Bump, Coating Normal
Octane Universal Material // Thin Film Channel
The Thin Film Layer channel puts an iridescent oily sheen on the object. The more reflective the material, the more obvious the effect. Combining this with a Coating really helps it pop out. This effect is a little hard to art direct, but what it essentially comes down to is playing with both the channel's IOR and Red color slider (Green and Blue don't seem to do anything here). The IOR controls how far in toward the center of the object the colors go, and to some extent the color itself. The Red slider changes all the colors in the effect.
Substance map: Film Width
Octane Universal Material // Bump - Normal - Displacement Channels
The Bump, Normal and Displacement Channels are all for affecting the look of the surface of the object. Both Bump and Displacement use the same map (usually called a Height map). Normal uses a Normal map, which is easily recognizable by its blue/purple/green appearance. Bump and Normal create a "fake" bumpiness effect and do not affect the silhouette, and are very easy on the GPU. Normal has directional data that bump does not have, so it's often better for adding detail. Displacement pushes the geometry in or out and does affect the silhouette, but is GPU intensive. Displacement requires a Displacement node which controls things like the height. Images can be connected directly to the bump or normal inputs. Combining all three (Bump, Normal, Displacement) can give a really nice effect with different images in each.
Substance map: Height (for Bump and Displacement), Normal
Octane Universal Material // Opacity Channel
The Opacity Channel works similar to how the Opacity slider in Photoshop works. This is very different than Transmission, and is useful if you want to make a hologram or something that doesn't feel solid. Unlike Photoshop, you can start seeing the back side of the object through the front side as you reduce the Opacity slider, so there are some interesting effects that can happen here.
Substance map: Opacity or reversed Transparency
Octane Universal Material // Dispersion Channel
The Dispersion channel disperses the light (splits it into colors) in Transmission-type materials. It's most obvious in Specular type Transmission (see Transmission channel) - the effect in Thin Wall and Diffuse are both very minimal and usually not worth the render hit. Dispersion is pretty GPU-intensive, so be careful when using it. The coefficient float goes from 0 to 0.1, and it's not like a linear "amount" slider where .01 gives you twice the dispersion than 0.05. There's a bunch of mathy stuff going on, so it's best to just play around. A good strategy is to start at 0.05 and work from there to find the effect you're after. The IOR channel of the material also makes a big difference in how strong the effect is, as seen in the image above. You can get a nice look by faceting your shape as well.
Substance map: None
Octane Universal Material // IOR (Dielectric) Channel
The IOR Channel (IOR stands for Index of Refraction, and is sometimes just called Index) is split into two sections. The top half - Dielectric IOR, shown above - is for specular type materials (glass, plastic, pretty much everything that's not metal). There are good technical explanations out there, but as an artist, the effect is pretty much that the higher the IOR, the more the light bends and distorts as it travels through a Transmissive (glassy) object, and generally the shinier the object's reflections look. If you want a realistic material, check this list out and pick an IOR from there.
Substance map: IOR or Index
Octane Universal Material // IOR (Metallic) Channel
Metallic IOR completely overrides Dielectric IOR when the Metallic channel float is set to 1(which effectively gives you a metallic material). Metallic IORs are very different than Dielectric ones - It mostly affects the color of the material and reflection.

Artistic mode This is the easiest to use, and also default. None of the fields work in this mode, so ignore them. You just set the Albedo color and you're good to go. The downside to this being so easy is that it doesn't create very realistic metals - they always look like painted Christmas ornaments.

Color+IOR mode (nerdy) is kind of a hybrid of the other two. Have you ever thought to yourself "man, I wish I could make a metal that has the physical properties of Ytterbium, but was purple"? Well, now you can. Go to refractiveindex.info, select Ytterbium from the "book"(??) dropdown, and put the n value in the left field, the k value in the right field, and then choose a nice purple in the Albedo channel. Presto! You just invented purple Ytterbium - a Nobel surely awaits. You can also just mess with the sliders and Albedo color and make interesting metals.

RGB IOR mode (very nerdy - don't say I didn't warn you) is for when that inner material scientist in you comes out and you want the metal as realistic as possible. First, you need the wavelengths that correspond to R, G and B values. Luckily you know off the top of your head that the values are 650 (red), 550 (green) and 450 (blue). You then convert each of these from nanometers to micrometers (because only a total troglodyte would be caught dead using nm for this kind of calculation), and get R = .65, G = .55 and B = .45. Now you head back here again, and pick a metal. Now punch .65 into the wavelength field, and copy the n value and paste it into the left field of where it says Metallic IOR (it may not say it, but that's red). go back, copy the k value, paste it into the right field. Rinse and repeat for G (.55) and B (.45) values, and easy peasy, you have a realistic metal. 

That said, materials using this mode don't have to be realistic though, you can just start messing with sliders until you see something you like.
Substance map: IOR or Index
Octane Universal Material // Transmission Channel
The Transmission channel controls the transluceny/refractive nature (not Opacity - that's a different channel) of the material. The three different Transmission Types produce very different effects. Specular is mostly for solid glass or translucent plastic. Diffuse is for marble, thick semi-translucent plastics, wax, etc. Thin Wall is for something like a soap bubble or very thin plastics or glass (blown glass ornament, etc). The Transmission color controls the intensity and color of the effect (black = no effect). Albedo should be set to black/float=0 to start with, but adding some in (low values) can create interesting effects. As Albedo approaches white, it negates the Transmission effect more and more.

Transmission is greatly affected by Dielectric IOR (see the IOR section above), and is also the starting point for Scattering and Absorption materials in the Medium channel (see the Medium section below).
Substance map: Transmission
Octane Universal Material // Emission Channel
The Emission Channel turns your material into a light source. Emission works with Albedo, Specular and Metallic, but usually you'll want to zero them all out (set color to black and float to zero) and focus the material on the light itself. The Emission Channel requires an Emission node hooked up to it to work at all. There are two types:

Blackbody Emission is a physically accurate light source. There's some scientific reason it's called that, but just think of it like the light types in a hardware store. The color of the light is determined by the temperature. A warm light like a candle (1,900K) or an incandescent bulb (2,800K) is on the low end of the spectrum. Octane's default white is 6500K. Above that it starts getting more blue, with stars getting up to 12,000K (Octane's max) and beyond. Power plays into this a lot too - if the power is high, the visual difference between 6500K and 12,000K is almost nothing, but as you drop the power, you start to see the color come out.

Texture Emission This is far easier to art direct, since you can just say "I want a green or pink light". You can pipe anything into the texture section (like the checkerboard seen above) and produce some cool effects. Generally you'll want to put either an RGB Spectrum node in, or a Gaussian Spectrum node. RGB is easy to visualize and good if you want the light itself to look like the color it's casting. Gaussian is trickier because you can't just pick a color - you have to be all sciency about it (read: play with sliders until you get what you're after), but it does produce better results for neon, as seen in the image above. Dobromir Dyankov has a terrific writeup about this.

Note about Camera Imager settings - There are three settings in particular you want to pay attention to for emissive materials - Bloom in the Post section is what gives lights their patented Octane Glow. Saturate to White in the Camera Imager section makes it so the light itself starts turning white as it gets hotter, which can be seen in real life neon and the like. Hot Pixel Removal, also in the imager, helps a lot to get rid of fireflies (super bright pixels that cause 3D artists to cry when they see them).
Substance map: Emission
Octane Universal Material // Medium Channel
The Medium channel controls the scattering and absorption of light inside a Transmissive material, particularly the Specular and Diffuse types. The Medium input needs one of the four Medium nodes available to work. We're only going to cover three of them here - the Volume medium node is a bit too advanced for this writeup. Lighting is very important for making this effect worth the render time it costs (which can be significant). Concentrate on back or side-lighting your objects for best results. Also consider using the Denoiser - it will drastically cut down on the render time to get a clean result.

Absorption Medium: As light passes through the object, the material absorbs certain wavelengths from that light (based on the absorption color you give it). When it absorbs a color, what's left is the opposite color. So in the image above, both the Specular and Diffuse materials have a blue absorption color, so what's left is orange. There's an "Invert Absorption" checkbox if that's too confusing, which would make it so if you choose blue, the object looks blue. Play with the Density value to get different looks. Absorption does not scatter the light or otherwise play with the refraction, so it's a pretty quick effect to render compared to the other mediums.

Scattering Medium: As light passes through the object, it scatters around and creates a milky, semitransparent effect. This is known as Subsurface Scattering in a lot of programs. This is very GPU-intensive, especially with the Specular Transmission type, so be wary of using it. The Scattering Medium node also allows for an Absorption color, so you can have both effects going on at once. Play with the Density value to get different looks.

Random Walk Medium: Similar to the Scattering Medium, but much more efficient and often better looking. In addition to Density, there's also Radius and Bias to play with. Choose the thinnest part of your object, roughly measure the density with a cube, and then set the radius to that as a starting point. Then adjust up or down according to what kind of look you want.
Substance map: Absorption, Scattering, SSS
There are a few other odds and ends that I didn't cover (notably the Material Layer, Round Edges and some of the stuff in Common), I might add those in later, but this should give you the information you need to go and make your own materials using the Universal Material.

All the materials I used to make this guide (as well as the Jedi Training Shaderball I modeled) are in a file I'm releasing this file as CC0, so go ahead and use them for whatever you'd like.

Octane Universal Material - Guide + Starter File
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