SACH · Carrier register
Carrier dossier: Scent sachet
The cheapest per month of any passive carrier, and the only one that works as an event rather than an atmosphere: it reads strongest in the two seconds after a drawer or a wardrobe door opens. Filler choice, load, and when a refresh stops being worth the oil.
By The Scent Desk·Published 2026-09-29
| Medium | scented filler (silica, vermiculite or cotton wadding) in a woven or paper pouch, 20-60 g |
|---|---|
| Release mechanism | very large surface area to volume ratio, so output is low per gram but extremely even |
| Where it wins | cheapest per month of any format, ideal for enclosed spaces, no vessel to break, easily refreshed |
| Where it fails | output too low for open rooms, fabric can stain if the pouch is torn, needs replacing rather than refilling |
| weight g | 20–60 |
| filler mesh mm | 1–4 |
| oil load pct | 10–22 |
| release days | 30–75 |
| coverage m2 | 1–5 |
How the four fillers actually differ
| Filler | Oil retention | Moisture uptake | Release curve | Suits |
|---|---|---|---|---|
| Silica | High | High | Strong first 3 days, then flat | Dry, sealed spaces |
| Vermiculite | Medium | Low | Flattest of the four | Swinging humidity, kitchens |
| Cotton wadding | Low | Medium | Very slow, long tail | Long-term sealed spaces such as wardrobes |
| Wood shavings or charcoal | Low | High | Erratic | Not recommended where dose control matters |
The choice follows directly. Stable humidity points to silica, which costs least and holds most oil. Swinging humidity points to vermiculite. A very slow release points to cotton wadding.
Load, and the transfer risk
Load is the weight of fragrance divided by the weight of filler. Safe ranges:
- Hung free, no fabric contact: 16-22%
- Possible fabric contact: 10-14%
- Sitting among clothing: 8-11%
Above the range, free oil appears on the filler surface and leaves a mark on whatever it touches that will not wash out. Wool and silk are the most sensitive, cotton next, and synthetics the least — though a mark on a synthetic is the hardest of all to remove. Wardrobes are therefore specified below 11% without exception.
Release window and when to replace
A sachet decays non-linearly. It gives up about 30% of its oil in the first 20% of its life and only about 15% in the last 30%. That is why "it stopped smelling" usually arrives around 70% of the nominal life rather than at the end.
Replace on the read at 20 cm, not on the calendar. If it is silent at 20 cm, it is finished.
Refreshing works but changes the curve. The first refresh, adding 3-5% of the filler weight in oil, restores about 80% of output; the second about 55%; from the third the filler stops absorbing and all the added oil sits on the surface, where the transfer risk rises sharply.
Why the outer fabric matters more than people expect
The outer sets the ceiling on release rate. Measured with identical filler and identical load:
| Outer fabric | Relative release rate |
|---|---|
| Non-woven | 100% |
| Light cotton | 85% |
| Tight-weave cotton | 60% |
| Coated canvas | 25% |
Coated canvas is barely breathable, and a sachet built on it reads as almost nothing unless you press your face to it. It is the commonest product defect in this format. Buy non-woven or light cotton.
Container compatibility, cleaning and disposal
- No container needed. Hang on a hook or ribbon; if laid flat, put a sheet of paper underneath to keep oil off lacquer.
- Cleaning is not possible. Filler that has taken oil cannot be washed, and the outer can be washed but should not be — detergent residue reacts with the next fragrance.
- To change direction, replace the whole sachet. The old oil cannot be cleared out of the filler, and mixing produces an unidentifiable middle note.
- Disposal: oil-bearing filler does not belong in a sink or a compost bin. Seal it and put it in general waste.
When not to choose it
- Covering more than about 6 m2. A sachet tops out near 5 m2.
- A room that has to smell on entry. A sachet is an event carrier, not an atmosphere carrier.
- Spaces above 70% humidity, such as a shower zone. Silica and wood fillers both absorb moisture and give it back, and the read swings violently.
- Replacement cycles longer than 60 days. Cotton wadding reaches 52 days and the others fall short of it.
Refill and replacement
Refresh by adding 1-2 ml of oil to the filler and shaking the pouch in a bag for a minute. Beyond the second refresh the filler stops holding.
Plans using this carrier
| Rooms | Rung | One fill lasts | Running cost |
|---|---|---|---|
| Entryway | L2 | 34 d | CNY 11 |
| Kitchen | L2 | 28 d | CNY 10 |
| Wardrobe | L1 | 52 d | CNY 13 |
Assembly, in order
- Pick the filler for the room — Vermiculite holds its release when the air is damp; silica beads pull moisture in and go quiet. Between a bathroom and a wardrobe the same pouch behaves like two different products.
- Place it side-on, never flat — Stand the pouch against a side wall or hang it. Lying flat on a drawer floor, the lower face is against the wood and half the surface does no work at all.
- Squeeze it once a month — Squeeze the pouch once a month to break up the filler. It costs nothing and it is the difference between an even curve and a flat final fortnight.
- Refresh twice, then replace — Add one to two millilitres of oil, close the pouch in a bag and shake for a minute. After the second refresh the filler stops holding and the whole pouch should be replaced.