Build a Performance Modpack from Scratch

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Goal

Create a Fabric 1.21.4 modpack with the essential performance mods — Sodium, Lithium, FerriteCore, and Iris for shaders.

Step 1: Create the Instance

1. Click + → New Instance.
2. Name it "Performance Pack".
3. Set Minecraft version to 1.21.4.
4. Choose loader Fabric.
5. Click Create.

Step 2: Add Performance Mods

Open the instance and go to the Setup tab. Search for and install each mod:

Core Performance

Optional: Shaders

Optional: Quality of Life

Step 3: Deploy

Click Deploy. Polymerium will:

1. Download Fabric loader libraries.
2. Download all mods to the shared cache.
3. Build the game directory with symlinks.
4. Download a Java 21 runtime if needed.

Step 4: Configure Memory

1. Go to Settings → Game.
2. Set Max Memory to at least 4 GB (6–8 GB if using shaders).
3. Or set it per-instance in the instance's properties.

Step 5: Launch and Play

Click Launch. The game starts with all performance mods active.

Step 6: Optional — Add Shaders

1. Download a shader pack (e.g. Complementary Shaders from Modrinth).
2. Move the shader .zip to persist/shaderpacks/ and create persist/shaderpacks/.keep so the directory is linked into the game. See Four-Layer Directories → for how persist/ works.
3. In-game, go to Options → Video → Shader Packs and select it.

Step 7: Save a Snapshot (Recommended)

Before you make further changes:

1. Go to Snapshots for this instance.
2. Click Create Snapshot.
3. Name it "clean-performance-base".

Now you can freely experiment — if something breaks, restore the snapshot.

What You've Achieved

• ✅ A clean Fabric 1.21.4 instance with performance mods
• ✅ Shared cache — these mods are available to other instances at zero extra disk cost
• ✅ A snapshot you can restore if needed
• ✅ Ready to add more mods on top of this base