Keeping The Sims 4 Fast With Lots of Custom Content

A bloated Mods folder is the main reason The Sims 4 starts crawling. Every package file in there has to be read when the game boots, when you open Create a Sim, and when you build a lot. The more files, the longer all of that takes, and past a certain point you’ll notice stutters, long load screens, and CAS taking forever to populate thumbnails.

The good news is you don’t have to give up your custom content to fix this. You just need to manage it instead of letting it pile up forever.

Why a large Mods folder slows loading and CAS down

The game scans every file in your Mods folder on launch, checking each package for conflicts, tuning overrides, and resource references. With a few hundred items this is fast. With tens of thousands of loose files, that scan adds real time to every boot.

Create a Sim is hit even harder. CAS has to generate thumbnails for every swatch of every item you have installed, every single time you open it fresh or clear the thumbnail cache. If you have thousands of hairstyles, clothes, and skin overlays, CAS can take minutes to fully load instead of seconds.

Clearing localthumbcache.package and other cache files

The Sims 4 keeps cached thumbnail and rendering data so it doesn’t have to rebuild everything from scratch each time. Sometimes this cache gets corrupted or just grows stale, and clearing it fixes weird graphical glitches, missing thumbnails, or CAS items that look broken.

1. Close the game completely.
2. Go to your The Sims 4 folder in DocumentsElectronic ArtsThe Sims 4.
3. Delete localthumbcache.package.
4. Also delete the files inside the cache and cachestr folders if they exist, but leave the folders themselves.
5. Launch the game. It will rebuild the cache automatically, so the first load after this will be slower than usual.

Do this occasionally, especially after adding or removing a batch of CC, not every single time you play.

Finding duplicates and content you never use

Over time it’s easy to download the same hairstyle twice from different sites, or keep CC you installed once and never actually use in a save. Every one of those files still gets scanned on launch even if you never touch it in game.

• Sort your Mods folder by file name or by the creator’s naming convention to spot near-identical files.
• Check subfolders you made months or years ago. People often forget what’s buried three folders deep.
• If you genuinely don’t remember downloading something, that’s a sign you probably don’t need it.
• Move anything you’re unsure about to a separate folder outside Mods so the game stops loading it. If nothing breaks and you don’t miss it, delete it for good.

Doing a cleanup pass every so often keeps the folder from quietly ballooning to a size that hurts performance.

Very high-poly CC and how it affects older PCs

Some custom content, especially hair, jewelry, and certain furniture, is built with a lot more polygons than the base game’s assets. This looks great in screenshots but costs more to render, especially with several Sims on screen at once wearing high-poly items together.

On a strong PC you might never notice. On an older or weaker machine, this shows up as frame drops in busy lots, slower rotation in CAS, and build mode lagging when you place a lot of detailed objects at once.

If your game chugs specifically during gameplay rather than just at loading, go through your CC and look for anything described by the creator as high-poly or high-detail. Keeping a mix of lower-poly basics alongside a few higher-detail pieces for special occasions is usually a good compromise instead of filling every category with the heaviest options available.

Merging package files: what it does and the catch

Merging combines multiple package files into one larger file using a tool built for that purpose. This cuts down the total number of files the game has to scan on launch, which speeds up loading noticeably if you have thousands of small CC items.

The benefit is straightforward: fewer files, faster scan, less strain on CAS when it’s generating thumbnails.

The downside shows up later. When a creator updates one of the items you merged, you can’t just drop in the new file and replace the old one, because it’s now buried inside a merged package alongside other content. You’d have to unmerge, find the specific item, update it, and merge again. For content you know gets updated often, like mods with ongoing bug fixes, it’s usually better to leave those files unmerged. Save merging for static CC like clothing, hair, and objects that creators rarely touch again after release.

Adding new CC in small batches and testing

The safest way to grow your CC collection without wrecking performance or stability is to add things gradually and check that everything still works before moving on.

1. Download a handful of new items at a time rather than fifty at once.
2. Launch the game and check that it starts normally and CAS opens without errors.
3. Play for a bit to confirm nothing is causing crashes, missing meshes, or odd behavior.
4. Only then add the next batch.

This way, if something does go wrong, you know exactly which small group of files to check instead of digging through everything you added in one giant session. It also means you notice performance creeping down gradually instead of one day finding the game unplayable with no idea which item caused it.

Combine this habit with periodic cache clearing and occasional duplicate cleanup, and a large CC collection stays manageable instead of turning into a mess you’re afraid to touch.

Questions people ask

How much custom content is too much for The Sims 4?

There's no fixed number, it depends on your PC and the type of content, but once your Mods folder reaches several gigabytes or tens of thousands of files, most players start noticing slower loading and CAS.

Will clearing localthumbcache.package delete my mods?

No, it only removes cached thumbnail and rendering data, not your actual mod or CC files, and the game rebuilds the cache automatically on the next launch.

Does merging package files break mods?

Merging itself doesn't break mods, but it makes updating individual merged items harder later, so it's best used on CC that creators rarely update.

Why does Create a Sim take so long to load with lots of CC?

CAS has to generate a thumbnail for every swatch of every installed item, so a large wardrobe of custom clothing and hair directly increases that loading time.

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