4mm is the standard cuff thickness on all Fractal Umbra sizes, by adding this free listing to your order you will get it with the 3mm cuff . 4mm is a bit more supportive than the V1s or V2s 3mm is going to be more similar, very bendy and most similar to V1s or V2s.
This Upgrade listing was only meant to be purchased along with a Fractal Umbra skeleton.
