---
title: Build a Performance Modpack from Scratch
description: A step-by-step guide to creating an optimized Fabric modpack with essential performance mods.
---

## 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

| Mod | What It Does | Search |
|-----|-------------|--------|
| **Sodium** | Modern rendering engine — massive FPS boost | `modrinth:sodium` |
| **Lithium** | Server-side optimizations — faster tick processing | `modrinth:lithium` |
| **FerriteCore** | Memory usage reduction | `modrinth:ferrite-core` |
| **Fabric API** | Required dependency for most Fabric mods | `modrinth:fabric-api` |

### Optional: Shaders

| Mod | What It Does | Search |
|-----|-------------|--------|
| **Iris** | Shader pack loader (requires Sodium) | `modrinth:iris` |

### Optional: Quality of Life

| Mod | What It Does | Search |
|-----|-------------|--------|
| **Mod Menu** | In-game mod list viewer | `modrinth:modmenu` |
| **Roughly Enough Items** | Recipe viewer | Search "REI" on Modrinth |

## 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 →](/docs/concepts/four-layers#persist---user-managed-persistence) 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
