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May 10, 2025 · 5 min read · TradeUpX Team

Best Filler Skins for CS2 Trade-Ups 2025 — Cheap, Liquid, Full-Range

In CS2 Mixed Float trade-ups, filler skins serve a precise role: they allow you to fine-tune the average adjusted float of your 10-skin contract without spending much money. The ideal filler skin is cheap, has a full 0.00–1.00 float range (so it can be obtained at any float), and has enough market liquidity that you can actually buy it. This guide covers everything you need to know about selecting filler skins.

What Makes a Good Filler Skin?

A filler skin in a trade-up contract is a skin from the same rarity tier that you use alongside your main skin to hit a target average adjusted float. The ideal filler has:
  1. Full float range (0.00–1.00): So you can choose any float you need for the calculation. Skins with capped ranges (like MP5-SD | Kitbash at 0.00–0.80) limit your options.
  2. Low price: Fillers are a means to an end. The cheaper, the more of your budget goes to main skins.
  3. High liquidity: If you need a filler at exactly 0.089 float, you need to find one on the market. Liquid skins with many listings are much easier to source.
  4. From the right collection: Fillers from the same collection as your main skin increase that collection's output weight — sometimes significantly improving EV.

Top Filler Skin Collections

The best filler skin collections combine cheap, full-range skins with good market depth:

The Fracture Collection

One of the best sources of Mil-Spec fillers. Several skins with full 0.00–1.00 float ranges, high market volume, and consistently low prices — making them easy to source at exact floats. Top choice for Restricted → Classified mixed-float contracts.

The Genesis Collection

Excellent Mil-Spec filler options with strong liquidity. Genesis skins tend to have tight float distributions and stable prices, which makes them reliable for precision float targeting.

Mixed-Collection Contracts

When your main skin and filler come from different collections, the output pool is split between both collections proportionally. For example: 7 main skins from Collection A + 3 fillers from Collection B = 70% chance of an A output, 30% chance of a B output. This is a core mechanic to understand — sometimes deliberately mixing collections gives you access to a better output pool at lower cost. Important: TradeUpX automatically searches for the best filler skin per contract based on liquidity, price, and float range. Enable Mixed Float mode to see filler skin suggestions.

Skins to Avoid as Fillers

  • MP5-SD | Kitbash (0.00–0.80 cap): Cannot achieve Well-Worn or Battle-Scarred. Limits your float targeting.
  • Desert Eagle | Heat Treated: This is a Limited Edition skin that cannot be used in trade-ups at all. TradeUpX filters it out automatically.
  • StatTrak skins as fillers for normal contracts: You cannot mix StatTrak and non-StatTrak skins in the same contract. All 10 inputs must be the same type.
  • Souvenir skins: Cannot be used in trade-ups at all.

How TradeUpX Selects Filler Skins

In Mixed Float mode, TradeUpX runs an exhaustive search: every valid main skin at your configured main float is tested against every valid filler skin at your configured filler float. The algorithm prioritizes:
  1. True full-range skins (0.00–1.00) — so the filler is achievable at any float
  2. Liquid skins with ≥3 marketplace listings
  3. Lowest total cost for the contract
  4. Highest ROI after Steam fees
The same-collection constraint: if your main skin and filler are from the same collection, that collection gets 100% output weight (10/10 inputs from it). This can dramatically change output probabilities vs. a mixed-collection contract.

Frequently Asked Questions

Can I use any skin as a filler in a CS2 trade-up?
The filler must be the same rarity tier as your main skin. Souvenir and Limited Edition skins cannot be used. For Mixed Float strategies, you also need the filler to have a float range that includes the float you need.
Does the filler skin collection affect trade-up output?
Yes — this is one of the most important mechanics to understand. The output pool is built from every collection in your 10 inputs, weighted by how many skins come from each. 7 from Collection A + 3 from Collection B = 70% chance of A outputs, 30% chance of B outputs. When your filler skins come from a different collection than your main skins, you're mixing the output pool. TradeUpX calculates the weighted EV for every combination automatically.
Which collections have the best filler skins right now?
The Fracture Collection and Genesis Collection are currently among the top choices — cheap Mil-Spec skins with full 0.00–1.00 float ranges and strong market liquidity. The best option shifts with market prices, so TradeUpX always scans live data to find the cheapest valid filler for each contract.
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