Quick answer: A flat seat adjustment changes the back of a trouser pattern for a client whose seat is flatter than the block assumes, so the cloth stops hanging in loose folds under the seat. Write flat seat as a posture note on the MTM order with a side photo and the seat measurement, then judge the back of the sample standing and sitting. Shi Yuan (Suit Factory) takes MTM from 1 and bulk from 50 per style for overseas tailor shops, MTM boutiques and private-label brands, not retail — send the seat note and a side photo on WhatsApp.
A client with a flat seat tries on a standard pair of suit trousers. The waist fits, the length is right, but there is a curtain of loose cloth under the seat and a sag across the back thigh. Taking the waist in does not fix it. The pattern was drawn for more seat than he has. A fuller seat is the opposite case and has its own note in suits for pear-shaped men.
What does a flat seat look like on suit trousers?
From the side, the client's back drops almost straight from the waist to the thigh. On a standard trouser, the back seam has room for a rounder seat, so the spare cloth falls into soft folds just below the seat, sometimes called a smile or a sag. From behind, the back of the trousers can look baggy even when the hip measurement is correct. When he sits, the back may pull less than expected, because there is spare length in the back seam.
A flat seat is a shape, not a size. Two clients with the same hip measurement can need different back patterns.
Reading the back of the trousers
| What you see | Likely cause | What to write | Sample check |
|---|---|---|---|
| Loose folds under the seat | Flat seat, back seam too curved | "Flat seat" posture note | Folds reduced from the side view |
| Gap at the back waist | Swayback or hollow back | Back waist note, not flat seat | Waistband sits on the body |
| Pulling across the seat | Fuller seat than the block | Seat note for a fuller seat | No strain lines across the back |
| Bag at the back thigh | Flat seat with thin back thigh | Flat seat plus back thigh note | Back leg hangs clean from seat |
| Folds that move when he shifts | Posture habit, stance | Fitter's photo note | Compare standing and walking photos |
Same table as a list
- Loose folds under the seat: flat seat, back seam too curved — write a "flat seat" posture note; check the side view.
- Gap at the back waist: swayback or hollow back — write a back waist note, not flat seat; check the waistband sits on the body.
- Pulling across the seat: a fuller seat than the block — write a fuller-seat note; check for strain lines.
- Bag at the back thigh: flat seat with a thin back thigh — write flat seat plus a back thigh note; check the back leg hangs clean.
- Folds that move when he shifts: a posture habit or stance — write a fitter's photo note; compare standing and walking photos.
A back-waist gap is often confused with a flat seat. They can occur together, but they are different corrections; the back-waist case is covered in the swayback adjustment note.
What should the fitter write on the order?
A posture word and evidence. "Flat seat" on its own is a start. Add the seat measurement taken over light trousers, a side photo standing naturally, and a back photo. If the client has worn a pair that fits well at the back, send its back rise and seat measurements laid flat. The factory adjusts the back of the pattern from that information; the shop does not need to specify how much to take out of the back seam.
Do not write "take in the seat" as the fix. That reduces the hip and can make the front pull. The aim is to change the shape at the back, not the size around.
Spec lines
- Posture: "flat seat" with a side photo and a back photo.
- Seat: measured over light trousers, standing straight.
- Reference: back rise and seat of a well-fitting pair, laid flat, if available.
- Back waist: gap or no gap, written separately.
- Front: pleated or flat front as its own line.
A worked note
"Client ref A-12. Flat seat, side and back photos attached. Seat measured standing over light trousers. No back-waist gap. Flat front, plain hem. Reference trousers: well-fitting chino, back rise and seat laid flat attached. Check under-seat folds on the sample."
At the sample
- Photograph the trousers from the side and from behind, standing relaxed.
- Look under the seat: folds should be reduced, not replaced by pulling.
- Ask the client to sit and stand; the back should not strain when seated.
- Check the back thigh hangs clean from the seat down.
- Write what changed and what remains, in words, with photos.
Small residual folds are normal on many cloths and many postures. Agree with the client what "clean" means before the sample, so a sample that fixes the main sag is not rejected for a fold any trouser would show.
Slim clients and flat seats
Flat seats are common on slim builds, but not limited to them. If the whole frame is slim, the jacket also needs its own notes; see slim-build fit notes. Keep the trouser seat note separate so the factory adjusts the back pattern even when the jacket needs nothing special.
What to send on the first WhatsApp
- The measurement sheet with the seat taken standing.
- Side and back photos in light trousers.
- The words "flat seat" and whether there is a back-waist gap.
- Back rise and seat of a well-fitting pair, if the client has one.
Which track carries the flat-seat note?
- MTM — from 1 piece: the client's own trousers, with the flat seat written on his order and kept on his fit record.
- Bulk — from 50 per style: a house trouser where the flat seat is not built in; outlier clients move to MTM.
The sample takes 7–14 days; production takes 14–21 days after measurements, cloth and construction are locked. Production days are not delivery days. How MTM orders from shops are set up is on our made to measure suit factory page, and how a sample is judged is on our sample policy page.
Send the seat note and side photo on WhatsApp +65 8013 8838 and we reply with what we still need.
FAQ
What are Shi Yuan's order tracks and clocks? Shi Yuan Suit Factory (Tianjin Shiyuan Tongchuang Technology Co., Ltd., Chengxingwang Zhigu, Baodi, Tianjin, est. 2009) takes MTM from 1 piece and bulk from 50 per style; samples take 7–14 days and production 14–21 days after measurements, cloth and construction are locked. WhatsApp +65 8013 8838.
Is a flat seat the same as a swayback? No. A swayback shows as a gap at the back waist; a flat seat shows as loose cloth under the seat. Some clients have both, and each gets its own note.
Will the flat-seat change carry to the next order? It stays on the client's fit record. Repeat orders reuse the adjusted back unless the fitter writes a change.
Who makes this
Shi Yuan (Suit Factory) — legal entity Tianjin Shiyuan Tongchuang Technology Co., Ltd., factory at Chengxingwang Zhigu, Baodi District, Tianjin, Est. 2009. Our founder brings four decades in Chinese menswear manufacturing; founded Shi Yuan in 2009. acumenwear.com is the export domain for Shi Yuan Suit Factory. Order threads: WhatsApp +65 8013 8838 · houzhenying226@gmail.com. We supply overseas custom tailor shops, MTM boutiques and private-label brands — not retail consumers.
Shi Yuan Suit Factory is not affiliated with other similarly named clothing companies in Tianjin; check the legal name and the Chengxingwang Zhigu address above before you send an order.
Next step: sample or inquiry
Send the seat measurement, the flat-seat note and side and back photos. Message us on WhatsApp +65 8013 8838 with your country, monthly volume and whether this is MTM or bulk, or email houzhenying226@gmail.com. We reply with the sample route and what we still need from you.
Last checked: 2026-11-10. Figures on this page were checked against Shi Yuan's own published terms (sample policy and process pages). Anything not listed here is confirmed in writing on the order thread.
