What does UD, 3K, 12K carbon mean and how do they differ?

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UD, 3K and 12K specify the carbon weave pattern. 3K means there are 3,000 filaments per "tow", 12K means there are 12,000 and UD means unidirectional (no pattern):

enter image description here

The construction of bike parts is always UD, only the top layer when naked can be specified to these different finish types. Also there is usually an option to choose between matte or glossy. Matte results in more stealthy look, glossy will make the pattern pop:

enter image description here

When the frame is painted it's UD underneath (usually branded frames are all painted).

As for physical properties, UD is the strongest, then there is 12K and last 3K. The finish is only the top-layer so the differences are only cosmetic.

You can also encounter a 18K weave (usually on road rims) which looks like this (glossy/matte). Its similar to 12K (but a bit bigger) and you can also see how a seam looks like:

enter image description here

12K is well recognisable from distance, 3K and UD you can differentiate when standing closer and they also usually look better up close than 12K (there are more visible irregularities in 12K weave than 3K up close). This is how 3K looks up close:

enter image description here

  • I thought very high end bikes use directional weave, which is stronger in a single direction.
    – Aron
    Commented May 31, 2015 at 6:28
  • 1
    @Aron yep that is the unidirectional = single direction.
    – Jerryno
    Commented May 31, 2015 at 15:04
  • Are the carbon fibre frames meant to be painted, or can they be used as they are? Commented Sep 11, 2016 at 19:42
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    @DmitriNesteruk can be used as they are. Most people install protective clear tape where some rocks can hit the frame to protect it better. Paint won't protect the frame much, it's just for aesthetics.
    – Jerryno
    Commented Sep 11, 2016 at 20:32
  • 1
    @DmitriNesteruk you might want to read this forum: chinertown.com (if you didn't already). There are build logs and good information about chiner frames.
    – Jerryno
    Commented Sep 12, 2016 at 14:51

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