@Unit23
Yeah it seems physics does not respect a 'root' of the hair vs its ends, it more sees, like you say, the entirety of the hair groom as a single-unit object with Niagara particles being handled independently.  Such that, if any particle section, be it end-of-strand or root-of-strand, starts or is moved beneath the physics object, it will pass through while enacting its own physical movement. 
And right, if you have a gown on too it complicates your decision-making because both groom and gown are now working with a single capsule-collision scheme.  
THX

Bassline, I was imagining the physics capsule would know the difference between root and end, and then apply the physics to the root and then from there repel and further length end of the strand.
But it may not work that way, its like it probably sees the hair as always-centered independent particle segments.  Like being on a sphere, you are always at the center, from your perspective.
And you know what the problem is, you can't paint cloth-like weight dynamics on the groom like you can with cloth.

Thats very interesting.
I am testing collisions right now , trying convex hulls instead of capsules.

The other thing are the particles of each hair strand , I used 8 but I can increase it up to 32 maximum , so 32 particles multiplied with 43.000 hair strands , that will cost computing power.
I've also noticed that the physics are working different when rendering or realtime.

This depends on your collision settings, of the character mesh, the character capsule, and the object it physically should interact with. If you have additional gear attached which goes beyond the capsule boundaries, they usually go through. Though, gear can also have its collision set - it really comes down to your needs and how you approach collisions.

Be aware that the character usually does not uses physic simulations, if enabled requires a hall array of character related settings to change, in order to work properly. 
If you use the Unreal inbuild cloth tool for hair, it will respond to your character mesh, assigned physics asset. A tweaked one is available on the market here https://www.unrealengine.com/marketplace/en-US/product/active-ragdoll However, the default physics asset usually is good enough, or only requires small tweaks (resizing upper body capsules of the physics asset)

Advanced physics can be seen in the addon I linked above, outlined in this video https://www.youtube.com/watch?v=WIHPF0XgosI

 

 

You know, don't go adjusting on my count.  Though it is interesting that at default the capsules would let it right through.
But looks really really good, I doubt the average viewer would in fact notice.  

yeah I guess it's me , I was to lazy to fine adjust the capsules. I also had to create shoulder capsules and tweak the Niagara Collision physic settings.
I didn't find the time for it. But I will do an Update to see if I can get it right.

;-)

Hi Bassline, 
Do you know why the physics passes through the character?  Think this is just a limitation yet?
Like, it moves but it is passing through the shoulders and chest. 
(I see you modeled the hair with a rested avatar shape already, so it obscures it well in the A pose, but the actual hair is passing through the mesh.  It is not practicing good social-distancing.) 

Thank you very much, I will do:)

haha , I will send you some longer hair :-)  But you will have to use UE4.25/3 !

@Bassline 303
Very nice tutorial
Thank you very much
Many regards rosuckmedia
Unfortunately I only have the short hair from you:D:D

@wendy ,

If you want to test groom , I can send you some test hair.
Send me a PM.

Here is how to Activate Groom Physics in UE4.25 :