Sandustry Filters Explained

This page explains the mechanics. If you already know them and just want the setup for a specific pair of materials, the Filter Setup Finder will give you the configuration directly.

What a Filter is

The Filter costs 250 Gold at tier 1. You name one material in its configuration, and from then on it sorts everything that crosses it into two groups: one falls straight down through the Filter and is deposited below, the other rides along the top like a normal Conveyor Belt.

Which group is which is what the mode decides.

Two modes:

• Allow — the named material falls through, everything else rides on
• Block — the named material rides on, everything else falls through

Use Allow when the thing you are naming is the product you want — it drops out and everything else carries on. Use Block when the named material is the one you want to keep travelling and everything else should drop away. Allow is the common case, because you usually want one specific output pulled out of a mixed line.

Density decides what the Filter ever sees

This is the mechanic that explains most setups that “don’t work”.

A Filter pulls from the bottom of whatever is sitting on it. In a tall mixed pile, heavy things have already sunk and light things are riding on top — and the light ones never reach the Filter at all, even when the Filter is configured to let them through.

Every density the official wiki records, heaviest first:

Read the Matter type column first, then the density. Solid and Slushy behave the same way at a Filter — Wet Sand, Residue and Voidbloom are all Slushy and all sort normally. The Liquid and Gas rows are here to tell you where those materials sit in a mixed pile, not to be filtered in this order; for those you need the Advanced Filter, covered further down.

One row has no matter type at all. Void Seed’s official page records a density and leaves that field blank, so the column shows a dash rather than a guess — and the Filter Setup Finder does not offer it, for the same reason it does not offer the rows below.

Four more rows are their own case: Amethelis, Dry Amethelis, Void Petal and Snow are Wisps. For the first three the wiki says what that means — Dry Amethelis “in common with Amethelis, is a ‘wispy’ material and will drift as it slowly falls”, and Void Petal is described in the same terms. Snow carries the same matter type without any description of how it behaves, which is all the more reason not to assume.

Their densities still tell you where each ends up in a settled pile, but nothing official describes how a Filter handles a pixel that does not fall in a straight line — so the Filter Setup Finder deliberately does not offer any of the four rather than guess. Let them settle before you try to sort them.

Snow is the one to watch there, because it is the one you are most likely to have running: the Cryoblaster makes it endlessly, and it is a renewable water source. Whatever you do with it, that is not a Filter problem we can answer.

This table is only the materials the wiki gives a density. For all thirty-four — including the four it records as a range or leaves blank — see every material and what it turns into.

The rows marked as ties are the ones that will cost you an afternoon. Five materials sit at 150 — Sand, Seed, Snow, Wet Sand and Liquid Copper; Wet Seed sits at exactly the same 100 as Water — the tie that makes wet seed production awkward. A tie does not mean a Filter cannot tell them apart — it names one material, so it still separates by name. What you lose is the stacking that does the work for you: neither one settles below the other, so neither is reliably the one touching the Filter. The wiki says as much about wet seeds, which are Official“the same density as Water, meaning they can remain suspended in the water instead of sinking”. Feed a tied pair as a thin, well-mixed layer so both actually reach the Filter, and let the Allow setting do the sorting.

So for anything that does differ in density, the rule is: filter the densest material out first. Gold at 300 is the heaviest pixel in the game and always sits on the bottom, which is why “Allow Gold” is the most reliable filter setup there is and why every gold line starts with one. Take the heaviest out, then the next, and each separation stays clean.

There is one exception worth knowing. If a pixel is within 1 block of the Filter — that is 4 pixels — it can be pulled down through denser material to reach it. It is a genuine mechanic, not a rumour, but it is not dependable enough to design a line around. Feed a thin, well-mixed layer rather than counting on it.

Filters do not stop liquids or gases

The Filter’s own stats read OfficialBlocks Liquid: No and OfficialBlocks Gas: No. Anything in those states passes straight through regardless of how the Filter is configured. There is no setting that changes this.

Water is the case that catches people. It does not ride a belt and it does not respect your filter — it goes through and keeps going. What actually blocks liquid is Block, Conveyor Belt, Kinetic Press and Flux Emanator, so a plain belt is the tool for draining water off a line, not a Filter. Moving water covers where to put it instead.

The Advanced Filter (tier 4, 1,500 Gold) is the building that handles multiple element types at once, including liquids and gases. Reach for it when a liquid needs routing somewhere specific — not when it just needs to drain away, which a belt does for free.

Why your Filter jammed

This is the failure that looks like a bug and is not.

If a pixel that the Filter is letting through changes into something else while it is passing through, it stops dead. It will not fall the rest of the way, and the conveyor part of the Filter will not push it along either. It has to be dug out by hand, and every stuck pixel narrows the gap until the line stalls completely.

The usual cause is Water. Sand meets falling Water mid-transit and becomes Wet Sand; Seeds become Wet Seeds. Both wedge in the Filter.

The fix is upstream, not in the Filter settings: keep water out of the section where filtering happens. Separating wet sand and water walks through the full case.

The trick worth building

Put a solid Block directly beneath a Filter and material can enter but has no way out. It stays there.

The main use is trapping Lava. Set a Filter to allow Cinder only, block it underneath, fill it with Cinders and ignite them — the Cinders melt to Lava and the Lava is now held exactly where you put it. Run Residue along the belt over the top and it ignites on contact, giving you an auto-burner with no moving parts and no fuel cost. Full setup on the slag processing page, and how to move lava for getting the Cinders there in the first place.

The same property is also how lines get clogged by accident, so if a Filter is mysteriously full, check what is directly underneath it.

Related

• Sandustry Filter Setup Finder — pick two materials, get the configuration
• How to Let Wet Sand Through Without Letting Water Through
• Sandustry Slag Processing — the Lava auto-burner in full
• Sandustry Logic and Signals — sensors that read what a Filter has sorted
• Sandustry Conveyor Belts and Launchers — why one stuck pixel stops the whole pile