Tutorial — Hair Under Caps and Bonnets

Augmented Traveler local tutorial. Back to Grooms — Tutorials · cap as garment: Tutorial — Marvelous Designer Garment to MetaHuman Outfit · evidence: Tutorial — Period Hairstyles from Evidence · groom build: Tutorial — XGen Period Hair for MetaHuman

Many of our figures cover their hair: Quaker women's caps indoors, bonnets outdoors, sailors' caps and hats. Hair must flatten or disappear under them without poking through. This tutorial sets the rule for each case and each surface.

Draft. Epic documents groom physics collision against a physics asset, not against a cloth cap. There is no Epic guide for hair under headwear. The approach below is our plan; the groom artist and cloth artist test it on the first cap. Correct menu names here.

1. The rule: don't simulate hair against a cap

Approach When Cost
A. Cap-compressed groom variant (default) Cap covers most of the hair and stays on for the scene Low. One extra groom per figure/date
B. Hide covered groups Cap hides whole groups (bun, crown) Lowest. No new groom
C. Groom collision with a physics body Short, loose hair near a cap edge that must move Kiosk only; tune per shot
D. Cards only under the cap edge Headsets and phones Low

Hair under a real cap is pinned, oiled and still. Simulating it adds cost and risk for no visible gain.

2. What the period tells us

Consequence: an 1840s cap at the back of the head shows the centre part and the bands over the ears, and hides the bun. That makes approach A or B normal for Mitchell indoors.

3. Approach A: cap-compressed groom variant

  1. Get the cap first. The cloth artist models it in Marvelous Designer on the MetaHuman avatar, over a proxy of the finished hairstyle (Tutorial — Marvelous Designer Garment to MetaHuman Outfit).
  2. Export a cap proxy (static mesh, closed, slightly inside the cap's inner surface) to Maya.
  3. In XGen, duplicate the hairstyle as GR_<Figure>_<Year>_Hair_Capped.
  4. Add the XGen Collision modifier to the covered descriptions, colliding with the cap proxy. Or reshape the guides by hand so they lie under the proxy.
  5. Reduce the bun. Scale it down so it sits fully inside the cap crown.
  6. Delete what is never seen. Set density to zero where the cap fully covers the scalp (keep a margin at the cap edge).
  7. Keep the visible parts identical to the uncapped groom: parting, bands, hairline. Viewers compare them if the cap comes off.
  8. Export with the Groom Exporter and bind as usual. The cap is a skinned or cloth garment from the outfit pipeline.

Check: no strands show through the cap at kiosk distance (1–2 m) through a full head turn and nod.

4. Approach B: hide covered groups

If the groups were planned well (bun, crown separate), hide the covered ones:

  1. Export the cap-on version without those groom_group_id values, or
  2. Keep one groom and hide groups at runtime (method unconfirmed; check whether 5.8 exposes per-group visibility on the Groom component; if not, use approach A).

5. Approach C: collision (kiosk only)

  1. Groom Asset Editor → Physics → Enable Simulation.
  2. Assign a Physics Asset on the Groom component. Add a sphere or capsule body on the head bone shaped to the inside of the cap.
  3. Turn on Solve Collision. Tune Collision Radius, Static Friction and Kinetic Friction.
  4. Use it only for loose ends near the cap edge (ringlets under a bonnet brim, a sailor's hair at the collar).
  5. Test a quick head turn. If strands still pass through, go back to approach A.

6. Coordination with the outfit

Step Owner
Hairstyle proxy (simple mesh of the dressed hair) to MD Groom artist
Cap or bonnet draped over the proxy Cloth artist
Cap proxy back to Maya Cloth artist
Capped groom variant Groom artist
Cap, hair and head reviewed together in Unreal Costume designer + historian

7. Per surface

Surface Cap on Cap off
Kiosk (strands) Capped strand groom (A); collision (C) only for edge strands Full strand groom
PC-VR Capped strand groom if within budget Full groom
Quest / Android XR Cards from the capped groom; hidden areas removed before generating cards Cards
Phones Cards or mesh; consider texture-only hair under the cap edge Cards or mesh
Vision Pro Cards first Cards

Generate cards from the capped groom, not the full one, so no hidden cards waste triangles (Tutorial — Hair Cards and Groom LODs for Headsets).

8. Practice exercise

Take Mitchell's 1847 groom. Make a capped variant under a simple back-of-head day cap. Compare the two at kiosk distance: parting and bands must match exactly. Count strands saved.

9. Check before costume review

Sources