Hi Just want to add some more details to this issue.

the way I assign the aiStandardHair shader is:

1. select the strand hair shape node from operation stack

2. right click the hair in viewport and select "assign new material"

3. choose the aiStandardHair shader to assign

Then after I applied the change, I can see a new aiStandardHair shader is added in Hypershape window

but when I click on the strand hair shape node (as in the screenshot), the Arnold attribute is empty

Does that mean the material is created but not assigned to the strand hair? how could I fix that?

Thank you

here's the screenshot

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Attached Files:

arnold_is_empty.PNG (164362 bytes),

Ah, turns out I need to use Mtoa 5.4