Two size charts disagree about what a 23-inch head is. A general hat chart starts Large at 23.25 inches (59 cm), while one bonnet seller's own chart calls 23 inches Medium and Large at once, and 24 inches both Large and XL.
Momme weight, crown diameter and band circumference appear on some listings and are missing from others. Price is always shown, and it runs from about $6 to $110 on caps that photograph identically.
The letter on a label is not portable between sellers. The centimetre figure is.
The size to buy is the one your measured head circumference falls into on that seller's own chart, not the letter you wore last time. Measure with a flexible tape about 1/8 inch above the ears and across the mid-forehead.
| Size | General hat chart | One bonnet seller's chart |
|---|---|---|
| S | 52-55 cm (20.5-21.6 in) | 19-20 in (48-51 cm) |
| M | 56-58 cm (22-22.9 in) | 21-23 in (53-58 cm) |
| L | 59-61 cm (23.25-24 in) | 23-25 in (58-64 cm) |
| XL | 62 cm and above | 24-26 in (61-66 cm) |
Elastic is why that second column overlaps itself. A stretch band really does span two rows, which makes the letter useless as a specification.
Carry your figure in centimetres and inches, because sellers publish one or the other and rarely both.
Bonnets are sold in a narrow momme band, 19 to 22, with 22 the most common figure on named sellers' listings and 16 turning up on lighter styles. Momme (mm) measures how much silk sits in a given area, so that band is a density range, not a quality ladder.
25 momme shows up in buying advice and almost never on an actual sleep cap: a bonnet carries its weight on your head all night instead of lying flat under it.
Grade 6A, the top of a scale that runs down through 5A, is claimed by nearly every silk bonnet sold, and mulberry appears on the same listings. Both are self-declared: all they separate is sellers who state a spec from sellers who do not, and tussah rarely turns up on bonnet listings.
OEKO-TEX Standard 100 is the one badge with a checkable meaning. It puts a bonnet in product class II, for articles worn largely against skin, and its own text calls it not a quality label: it covers dye and finishing residues, not fit or life.
The alternatives to a silk bonnet each cost something specific:
- **Polyester satin.** Satin is a weave, not a fibre, so most satin bonnets are polyester. The American Academy of Dermatology names silk and satin together as gentler on hair than other materials, so the satin versus silk choice turns on heat and moisture, not slip.
- **Bamboo silk.** Sold as bamboo viscose or bamboo lyocell; one bamboo cap specifies a 600 thread count and OEKO-TEX certification.
- **Modal.** Against cotton, modal and bamboo both absorb more moisture and pass more air, which cuts both ways over damp hair: absorbency is not protection.
A made-to-order spec sheet for a custom bonnet lists what retail listings leave blank: panel count, seam placement, band assembly, single or double crown layer. Weight is the fallback tell: bonnets run 1.76 oz in satin to 8.47 oz.
A bonnet slides off when its elastic band is longer than your head needs, and it marks your hairline when the band is tighter than your scalp tolerates. Sellers print band circumference, 17 inches on Small through 21 on Large and XL, and almost none print band width.
Crown diameter is the second fit number, and it tracks hair volume rather than head size: 12 inches on standard styles, 13 on large, 13.8 at the top. Under two inches decides whether a pineapple survives the night or is flat by morning.
Band width would settle the tension question and almost no seller publishes it. Compare the printed circumference against your own measurement instead, and expect the band to stretch to your head rather than sit slack.
The American Academy of Dermatology gives the harder check: if your hairstyle feels painful, the style is too tight. Rubbing from a head covering can cause traction alopecia, the hairline shows it first, and untreated it can be permanent.
The academy's other prevention line is to pull hair back loosely beneath the covering, which makes how you put a bonnet on part of the tension answer.
Closure type decides whether either failure can be corrected after you have paid:
- **Fixed elastic band.** Simplest and least correctable. A 22-momme elastic-only model may not hold for restless sleepers or voluminous hair.
- **Tie band with anti-fall loops.** Adjustable in both directions, which is what keeps one bonnet below the pain threshold and above the slip threshold.
- **Buckle strap or clip.** Adjustable to a repeatable setting, so night forty matches night one.
Mulberry silk bonnets from established sellers start around $40 and run past $110. Polyester satin caps sell for roughly $6 to $16, often in multipacks.
| Price | What the listing states |
|---|---|
| $39.90 | 22 momme, Grade 6A, OEKO-TEX certified, one size |
| From $49 | 22 momme, Grade 6A |
| From $59 | 19-22 momme, grade undisclosed |
| From $110 | 22 momme, Grade 6A |
Nothing on that spec line improves as the price nearly triples. The extra money buys sizing options, construction and a brand, and the same cap is sold as a bonnet, a sleep cap or a nightcap depending on the seller.
Fine, straight, low-density hair is the easiest case: a 12-inch crown, the lighter end of the momme band, a tie band rather than heavy elastic, at the bottom of the silk range.
Curly and coily hair pineappled on top of the head needs the 13 to 13.8-inch crown, which is where sizing options start costing real money.
Locs, braids and hair past the shoulder need length, not diameter. Long styles run to 26.8 inches, a different shape rather than a bigger size.
Colourways and a pleated front change none of this, so choose them last.
A listing that says only silk, with no fibre origin, no grade and no momme number, has given you nothing to check before paying. The absence is the signal.
Momme, crown diameter and band circumference are all printable, and the sellers who print them are choosing to be checkable. Band width is printed by almost nobody, which is why your own tape and one uncomfortable night are still the last word on tension.
