How CS2 Collections Feed Trade-Ups
Every skin in a trade-up belongs to a collection, and the collection is what decides which skins you can receive. Here is how that link works.
What a collection is
A collection is a themed set of skins released together — usually tied to a map, an operation, or a case. Each skin in a collection sits at a specific rarity tier, and most collections hold skins across several tiers. The collection a skin belongs to never changes, and it is the key fact a trade-up contract looks at.
Why collections matter for trade-ups
A trade-up does not pull from the whole game. When the contract picks one of your ten inputs to decide the result, it looks at that input's collection and hands you a random skin from the next tier up within the same collection. So the collections you feed in are the only collections you can possibly receive from.
If a collection has no skins at the tier directly above your inputs, it cannot be used as an input for that trade-up at all — there is nothing for the contract to produce.
Mixing collections changes the odds
You can split your ten inputs across up to two collections. Each input adds one entry to the draw, so the share of inputs from a collection equals the chance the result comes from it:
- All ten from one collection guarantees the output comes from that collection's next tier.
- Seven and three gives roughly a 70% / 30% split between the two collections.
- Within the chosen collection, the specific skin is then spread across that tier's candidates, generally treated as equally likely.
This is why people pick collections deliberately: a collection with fewer skins at the output tier concentrates the odds onto each candidate, while a crowded tier thins them out.
Picking a collection wisely
There is no single best collection — it depends on the relative value of the inputs versus the possible outputs, which shifts with the market. Community price databases publish estimates for these pools, but those figures move constantly, so treat any single number as guidance rather than a fixed fact.
Set your collection split in the CS2 trade-up calculator to watch the odds update live, then read how the contract chooses your output for the full mechanics.