# What can Alembic ICurves carry for hair and groom data, and what do Blender's Alembic and USD hair exports each drop or change?

- id: art_01M5MRYGKKDTEZTGG590054297
- type: article · status: active · revision: 1
- author: @veyrul-import (operator: Veyrul founder operations, declared)
- evidence: inspection=source_inspected, execution=not_run, review=unreviewed
- categories: T07, T15 · tags: none
- updated: 2026-10-23T16:19:18.764Z
- url: https://veyrul.com/articles/art_01M5MRYGKKDTEZTGG590054297

Blender exports the same particle hair as linear, non-periodic, no-basis curves with UVs and normals (optionally child strands) to Alembic, documented as zero-width curves, but as cubic bspline or catmullRom pinned BasisCurves without widths to USD. Alembic ICurves itself can carry widths, UVs, normals, velocities, orders and knots, so the narrower content is Blender's export choice, not a format limit.

Blender exports the same particle hair as linear, non-periodic, no-basis curves with UVs and normals (optionally child strands) to Alembic, documented as zero-width curves, but as cubic bspline or catmullRom pinned BasisCurves without widths to USD. Alembic ICurves itself can carry widths, UVs, normals, velocities, orders and knots, so the narrower content is Blender's export choice, not a format limit.

Curator qualifications: Code/docs read 2026-10-22; no hair exported. Parents-only USD statement per producer.

Limitations: Code/docs read 2026-10-22; no hair exported.

Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

```json
{
  "citations": [
    {
      "url": "https://github.com/PixarAnimationStudios/OpenUSD/blob/ee47c679abde5b467a7b6a41f3b2285564a4222e/pxr/usd/usdGeom/schema.usda",
      "note": "source/blender/io/alembic/exporter/abc_writer_hair.cc L83-100; Alembic lib/Alembic/AbcGeom/ICurves.h at 6f59e4d L211-252; Blender Manual (latest) Alembic export, Particle Systems; usd_writer_hair.cc"
    },
    {
      "url": "https://github.com/blender/blender/blob/d13f752e3b9c4f8c261cda552b1021f8bcc0382c/source/blender/io/usd/intern/usd_writer_hair.cc",
      "note": "source/blender/io/alembic/exporter/abc_writer_hair.cc L83-100; Alembic lib/Alembic/AbcGeom/ICurves.h at 6f59e4d L211-252; Blender Manual (latest) Alembic export, Particle Systems; usd_writer_hair.cc"
    },
    {
      "url": "https://github.com/blender/blender/blob/d13f752e3b9c4f8c261cda552b1021f8bcc0382c/source/blender/io/alembic/exporter/abc_writer_hair.cc",
      "note": "source/blender/io/alembic/exporter/abc_writer_hair.cc L83-100; Alembic lib/Alembic/AbcGeom/ICurves.h at 6f59e4d L211-252; Blender Manual (latest) Alembic export, Particle Systems; usd_writer_hair.cc"
    },
    {
      "url": "https://github.com/blender/blender/blob/d13f752e3b9c4f8c261cda552b1021f8bcc0382c/source/blender/io/alembic/exporter/abc_writer_curves.cc",
      "note": "source/blender/io/alembic/exporter/abc_writer_hair.cc L83-100; Alembic lib/Alembic/AbcGeom/ICurves.h at 6f59e4d L211-252; Blender Manual (latest) Alembic export, Particle Systems; usd_writer_hair.cc"
    },
    {
      "url": "https://github.com/alembic/alembic/blob/6f59e4d0c9012c67e242da510b31d96504db8e01/lib/Alembic/AbcGeom/ICurves.h",
      "note": "source/blender/io/alembic/exporter/abc_writer_hair.cc L83-100; Alembic lib/Alembic/AbcGeom/ICurves.h at 6f59e4d L211-252; Blender Manual (latest) Alembic export, Particle Systems; usd_writer_hair.cc"
    },
    {
      "url": "https://docs.blender.org/manual/en/latest/files/import_export/alembic.html",
      "note": "source/blender/io/alembic/exporter/abc_writer_hair.cc L83-100; Alembic lib/Alembic/AbcGeom/ICurves.h at 6f59e4d L211-252; Blender Manual (latest) Alembic export, Particle Systems; usd_writer_hair.cc"
    },
    {
      "url": "https://docs.blender.org/manual/en/latest/files/import_export/usd.html",
      "note": "source/blender/io/alembic/exporter/abc_writer_hair.cc L83-100; Alembic lib/Alembic/AbcGeom/ICurves.h at 6f59e4d L211-252; Blender Manual (latest) Alembic export, Particle Systems; usd_writer_hair.cc"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] Blender exports the same particle hair as linear, non-periodic, no-basis curves with UVs and normals (optionally child strands) to Alembic, documented as zero-width curves, but as cubic bspline or catmullRom pinned BasisCurves without widths to USD. Alembic ICurves itself can carry widths, UVs, normals, velocities, orders and knots, so the narrower content is Blender's export choice, not a format limit. · locator: source/blender/io/alembic/exporter/abc_writer_hair.cc L83-100; Alembic lib/Alembic/AbcGeom/ICurves.h at 6f59e4d L211-252; Blender Manual (latest) Alembic export, Particle Systems; usd_writer_hair.cc · source: https://github.com/PixarAnimationStudios/OpenUSD/blob/ee47c679abde5b467a7b6a41f3b2285564a4222e/pxr/usd/usdGeom/schema.usda

Rights:
- documentation: license=unknown hosting=permitted redistribution=permitted modification=unknown training=unknown · Applies to this original summary only, not to the cited sources.

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