Chemex Coffee Filters: Sizes & Types

Chemex coffee filters are heavier, thicker, and more particular than any other pour over filter on the market — and that's the whole point. The bonded paper traps fines and oils that lighter filters let through, producing the cleanest cup of any commercial brewer. This is the filter buying guide: what fits which Chemex, bonded vs unbleached, how to fold them, and what to do when you run out at 7 a.m.

What makes Chemex filters different

Chemex filters are 20–30% thicker than other pour over filters — three layers folded toward the spout, one layer on the other side. The heavyweight paper is "bonded" (the layers are pressed together) and tightly woven, which means it traps fines and oils that a V60 or Kalita Wave filter would let through. The cup that comes out is clearer, cleaner, and more aromatic than any other paper-filtered brew.

The trade-off is brew time and finickiness. Chemex filters drain slower (a Chemex brew takes 4:30–5:30 vs 3:00–3:30 for a V60), and a grind that works perfectly in a V60 will stall a Chemex. The filter is also rated for a specific Chemex model — using the wrong size folds incorrectly and either floods the brewer or leaves dry pockets. Match the filter to the brewer.

Sizing: which filter for which Chemex

Chemex model	Capacity	Filter size	Filter pack
3-cup Classic	15 oz	FS-100 (square, pre-folded)	100 ct / 40 ct
6-cup Classic	30 oz	FS-100 or FC-100 (square or circle, pre-folded)	100 ct / 40 ct
8-cup Classic	40 oz	FP-100 or FC-100 (pre-folded)	100 ct / 40 ct
10-cup Classic	50 oz	FP-100 (pre-folded)	100 ct
6-cup Funnex / Handblown	30 oz	FS-100 or FC-100	100 ct / 40 ct

The two most-common Chemex models — 6-cup and 8-cup Classic — both use the standard FS-100 (square, pre-folded) filters. If you have a Chemex but aren't sure which size, count the cup notches on the wood collar: 6-cup has three dots/divots stamped into the side; 8-cup has four. The filters are interchangeable between 6-cup and 8-cup if you're in a pinch, but the fold sits more cleanly in the model it's sized for.

Square vs circle filters

Chemex sells filters in two shapes:

Square (FS-100, FP-100): the original Chemex filter. Square sheets that fold into a cone with one side three layers thick and the other side one layer. Slightly more paper makes contact with the coffee bed, which contributes to the Chemex's slow, even extraction.
Circle (FC-100): introduced later. Circular sheets that fold the same way as squares but with less corner waste. Brews almost identically to squares; some pour-over fans report a marginally cleaner cup, but the difference is minor.

Either works. We use squares as the default because they're more widely stocked and the corner overhang doesn't affect the brew. Pick whichever your local store carries reliably.

Bleached vs unbleached

Chemex makes both:

Bleached white (default). Oxygen-bleached, which is a chlorine-free process — the paper is whiter than natural pulp without the chemical residue concerns of chlorine-bleached filters. Less papery flavor than unbleached. This is what most Chemex drinkers use and what we recommend.
Unbleached natural (brown). Same paper without the bleach step. Slightly more papery flavor — needs a thorough hot-water rinse before brewing to remove. The natural color appeals to drinkers who prefer fewer processing steps, but the flavor cost is real and the only way to compensate is a longer rinse.

How to fold a Chemex filter

Pre-folded filters (the standard packs) come ready to use — open them into a cone shape, three layers on one side and one on the other, and drop into the Chemex. If you only have flat sheets (some specialty packs ship this way), here's the fold:

Start with a square sheet. Place it flat on the counter.
Fold in half diagonally to make a triangle.
Fold the triangle in half again to make a smaller triangle.
Open one side by separating one of the layers, creating a cone with three layers on one side and one layer on the other.
Drop the cone into the Chemex with the three-layer side facing the spout. This is critical — the three-layer side supports the brew weight, and the spout keeps the brew flowing through it.

How to use a Chemex filter

Rinse before brewing. Chemex filters are heavier than other pour over filters and carry more papery flavor. Pour 200–300 g of hot water through the empty filter before adding coffee. Discard the rinse water and the pre-warmed Chemex is ready to brew. Skip this step and the first cup tastes like paper.
Match the three-layer side to the spout. The Chemex is asymmetrical for a reason — the three-layer side supports the brew weight; the single layer side prevents brew from sloshing out of the spout when you pour. Filter wrong-side-around and the cup can stall or splash.
Don't reuse filters. Chemex filters are designed for single-use. Reused filters have residual oils that taste rancid and structurally weaken after one brew.
Compost the spent filter and grounds together. Both biodegradable.

Where to buy Chemex filters

Chemex filters are stocked at most specialty coffee shops, on Amazon (Chemex Filters FS-100 / FP-100 are widely available in 100-count packs for around $12), and at kitchen retailers like Williams Sonoma and Sur La Table. Specialty coffee subscriptions sometimes include filter packs with quarterly shipments.

One word of caution: third-party "Chemex-compatible" filters from off-brand sellers vary wildly in paper weight and fit. The cup quality difference is real — original Chemex filters use a specific 24 lb paper that drains at the rate the brewer was designed for. Cheaper imitations often drain too fast and produce thin, under-extracted cups. Pay the extra dollar per pack and buy original.

Chemex coffee filters FAQ

What size Chemex filters do I need?

It depends on your Chemex model. The 6-cup and 8-cup Classic Chemex (the two most common) both use standard FS-100 (square) or FC-100 (circle) filters — these are interchangeable between those models. The 3-cup uses the same filters but with more overhang. The 10-cup uses larger FP-100 filters. If you're not sure, count the cup notches on the wood collar: 6-cup has three, 8-cup has four.

Can you use V60 filters in a Chemex?

Technically yes, but the cup quality drops noticeably. V60 cone filters are thinner and drain faster than Chemex bonded filters, so the brew runs too quickly and tastes thin. They also don't fit the Chemex geometry — the cone is too small and channels water down the sides instead of through the bed. Use proper Chemex filters; the marginal cost is small.

What's the difference between bleached and unbleached Chemex filters?

The bleached white filters are oxygen-bleached (chlorine-free) and carry minimal papery flavor — these are the default and what most drinkers use. Unbleached natural (brown) filters skip the bleach step and have a slightly more papery taste that requires a more thorough rinse to remove. The two are interchangeable; bleached is cleaner-tasting, unbleached is more "natural" in appearance.

Do you need to rinse Chemex filters?

Yes — Chemex filters are thick and carry meaningful papery flavor without a hot-water rinse. Pour 200–300 g of hot water through the empty filter before adding coffee, discard the rinse, and the Chemex is pre-warmed and ready. Skip this step and the first cup tastes like wet cardboard. Even bleached filters benefit from rinsing; unbleached filters require it.

Can you reuse Chemex filters?

No — Chemex filters are single-use. The paper is designed to filter once at a specific drain rate; after one brew, the filter is saturated with coffee oils that go rancid quickly and the paper structure weakens, so the next brew either stalls or channels. Use one filter per brew, compost it with the grounds.

Why do my Chemex filters drain too slowly?

Three likely causes: grind too fine (the most common — Chemex wants medium-coarse, one click coarser than V60), poured too fast and flooded the bed (slow the pour and pour in concentric circles, not a straight stream), or the filter is folded wrong-side-around (three-layer side should face the spout, not away from it). Re-check the grind first.

Are Chemex filters compostable?

Yes — both bleached and unbleached Chemex filters are 100% compostable along with the spent grounds. They break down within a few months in a standard backyard compost or a few weeks in a hot-composting setup. This is one of the cleaner pour-over disposal options compared to plastic dripper holders.