Product Code Guide
Calvin Lin
2009/12/14 (updated: 2026/07/19)
2009/12/14 (updated: 2026/07/19)
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Introduction
Every iSwim thong, brief, or swimwear comes with a unique product code — and it’s more than just an order reference. Our codes tell a story: when it was designed, what type of cut it features, and even which version of the back cut it includes. If you've ever wondered, “What does u3020 or s3011 actually mean?”, this guide is for you.
Product Code System
- iSwim’s underwear and swimwear codes reflect the design type and year of release.
- From 2009 to 2016, product codes consist of 6 characters. The first two digits indicate the year, and the third character shows the category: 'u' for underwear, 's' for swimwear.
- For example, 13u527 means it’s an underwear design from 2013, the 527th style since 2009.
- From 2017 onwards, codes are 7 characters long. The 4th character represents a subcategory:
1 — 15mm waistband
3 — 8mm strap
5 — bikini-type 8mm strap
7 — 15mm inset-style
Even numbers (2, 4, 6, 8) mainly used for special or experimental designs. Most are standalone styles, and some are released as limited editions. - An additional suffix indicates the back cut, such as -H1.
For example: 21u3009-H1 means it’s an underwear style u3009 launched in 2021 with a H1 back (Half-back, Super-low rise).
Back Piece Code System
- Since 2017, styles with a 4th code digit of 1, 3, 5, or 7 often allow back piece customization (some options may require an additional fee).
- New designs (from 2017) are not compatible with old designs (2009–2016), so back cuts like B1, H1, or Y1 cannot be applied to earlier versions.
- We offer a variety of back styles, ranging from sexy to playful. Each back type is available in four waist heights (Take Y-thong as an example) :
Y0 — low rise
Y1 — super-low rise
Y2 — ultra-low rise
Y3 — extreme-low riseY1 is the default height for most of our Y-thongs. Y0–Y3 are the same price and can be replaced for free.
Y5 is the default height for most Y-thongs with special narrow bottom cut. Y4–Y7 are the same price and can be replaced for free.
Since the Y5 must use a special front design, the Y1 cannot be replaced with the Y5.
iSwim Back Piece Codes & Styles
Even our back piece code chart is tailored with precision — because seduction deserves structure.
📱 The mobile version can swipe left and right to view the complete information
| Code | Name | Note |
|---|---|---|
| F1 | Full Back Brief | Slightly narrower than standard briefs, light coverage, hugs fitness-shaped butts |
| B1 | 3/4 Back Brief | Slightly less coverage than F1, covers around 75% of the butt |
| H1 | Half-Back Brief | Medium coverage, Rio-style Brazilian cut |
| A1 | Narrow Bottom Brief | Playful and minimal, narrowest bottom for a clean, sexy cut |
| ▲ The above back pieces can be interchanged for free (Includes C1, T1 and D1 thongs) | ||
| U1 | Smile Back Brief | Features a 'smile line' under the butt for flirty exposure |
| N1 | Mini Back Brief | Covers only 1/3 of the butt, with less smile line than U1 |
| J1 | Butt-Lifting Cutout | One-piece seamless cut for visual lift and clean contour |
| O1 | Open hole back | The central circular hole design is smaller than the J1 model, creating a more concentrated and simple visual effect. |
| ▲ Briefs | ▼ Thongs | |
| C1 | Cheeky Thong | Perfect for first-time wearers, designed to avoid uncomfortable wedgies |
| T1 | Standard Thong | Mid-width thong design for stability and fit (8mm version offers a tighter tease) |
| D1 | Upper Triangle Thong | Triangle cut on top enhances upper butt curves |
| Y1 | Y-Shaped Thong | Calvin’s top pick — perfect balance of fit and seduction |
| V1 | V-Shaped Thong | Perfect for rounder butts — with 2 extra inches of waistband for better lift. The 8mm version is our signature V-string |
| E1 | Triangle G-String | Upper triangle + G-string, 8mm T-back design |
| ▲ The above back pieces are available in four heights: 0, 1, 2, and 3. | ||
| G1 | Thin G-String | Available only in 8mm type, minimal visual impact |
| M1 | Double Loop Thong | 8mm twin strap design, comes in M0 / M1 / M8 height options |
| S1 | One-String G-String | Only in 3mm type, minimal and ultra-flexible — height adjusts freely with strap position |
Note：The above is based on the most common 1 - super-low rise as an example.
- Tail code ending in 4, 5, 6, 7 means additional handcrafted modification (extra charge applies) , whose heights correspond to 0, 1, 2, 3.
- The back pieces of Y4 ~ Y7 and V4 ~ V7 are special narrow-bottomed thongs with a special front piece design. Y5 can be replaced for V5 at an additional cost. However, due to the limitations of the front piece design, Y1 and Y5 cannot be replaced, and neither can V1 and V5.
- Most back styles are interchangeable or upgradeable (additional fees may apply). Please leave a note on your order if you'd like a custom combination — or consult our customer service for assistance.
More info 👉 Rise Position.
Product Code FAQ
What do the letters u and s mean in iSwim product codes?
The letter u represents underwear, while s represents swimwear. In product codes from 2009 to 2016, the third character identifies the product category, and the same basic category logic continues in later codes.
Do the first two digits of the product code indicate the design year?
Yes. The first two digits usually indicate the design year. For example, 21u3009 represents an underwear style introduced in 2021.
What do 1, 3, 5, and 7 mean in product codes from 2017 onward?
From 2017 onward, the fourth character identifies the subcategory. For example, 1 represents a 15mm waistband, 3 an 8mm strap, 5 a bikini-style 8mm strap, and 7 a 15mm inset-style design.
What do suffixes such as H1, Y1, and V1 mean?
These suffixes identify the back piece. For example, H1 means a super-low-rise Half-Back, Y1 means a super-low-rise Y-Shaped Thong, and V1 means a super-low-rise V-Shaped Thong.
What do the numbers 0, 1, 2, and 3 at the end of a back piece code mean?
They indicate different rise heights, from higher to lower: 0 is low rise, 1 is super-low rise, 2 is ultra-low rise, and 3 is extreme-low rise. Most compatible back styles are available in these four heights.
What do the numbers 4, 5, 6, and 7 at the end of a back piece code mean?
They indicate back pieces with additional handcrafted modifications. Their heights correspond to 0, 1, 2, and 3, and some options require an additional charge.
Can older styles from 2009 to 2016 use newer back pieces?
No. Designs from 2017 onward use a different pattern system, so newer back pieces such as B1, H1, or Y1 cannot be directly applied to older styles from 2009 to 2016.
Can Y1 be changed directly to Y5?
No. Y5 uses a special narrow-bottom structure and requires a different front piece design, so Y1 and Y5 are not directly interchangeable.
Can most back pieces be changed or upgraded?
Most styles introduced from 2017 onward allow compatible back piece changes or upgrades, but availability depends on the product pattern and construction. Some special back pieces or modifications may require an additional fee.
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