Understanding Different Types of Seams in Garment Construction

Time to read: 6 minutes

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Seams are one of the most overlooked—yet most critical—components of garment construction.

A seam is the join where two or more pieces of fabric are held together, usually with stitches. It transforms flat fabric pieces into a three-dimensional garment. But beyond shaping, seams must also be

• Load-bearing (when needed)

• Durable

• Comfortable

• Flexible (when needed)

• Compatible with the fabric type

• Low profile

Choosing the wrong seam can lead to bulk, seam failure, poor fit recovery, or production inefficiencies.

Let’s break down the main seam types and when to use them.

How Seams Are Classified (ISO 4916 Overview)

Seams are classified under ISO 4916 into eight seam classes based on how fabric layers are joined.

Class 1 – Superimposed Seams

Two or more fabric layers are placed on top of each other and stitched near the edge.

Common stitches:

• 301 lockstitch

• 401 chainstitch

• 500 class overedge

Common uses:

• Shirts

• Lingerie

• General garment construction

This is the most common seam class in apparel.

Class 2 – Lapped Seams

Fabric layers overlap and are stitched together.

Common uses:

• Denim

• Outerwear

• Heavy-duty garments

These seams are strong and ideal for load-bearing areas.

Class 3 – Bound Seams

A separate binding strip encloses raw edges.

Common uses:

• Necklines

• Decorative finishes

• Medium-weight fabrics

They create clean internal finishes and increase durability.

Class 4 – Flat Seams (Butt Seams)

Fabric edges meet edge-to-edge and are stitched flat.

Common uses:

• Activewear

• Underwear

• Knit garments

They reduce bulk and improve comfort.

Class 5 – Decorative Seams

• What it is: Stitching applied to one or more layers of fabric purely for visual and aesthetic purposes, rather than for structural joining.

• Common Applications: Pintucks, pleats, decorative topstitching on denim pockets, or embroidery details.

• Tech Pack Tip: Because these seams do not hold the garment together, their sole purpose is to look good. Your tech pack needs to be highly specific about the stitch length (SPI—Stitches Per Inch), thread weight, and thread color, as this seam is meant to be highly visible to the consumer.

Class 6 – Edge Finishing

• What it is: Stitching that encompasses the raw edge of a single ply of fabric to neaten it and prevent the yarns from unraveling or fraying over time. It does not join two separate garment pieces together.

• Common Applications: Overlocked/serged edges on the interior seams of a t-shirt, blind hems on dress trousers, and simple folded hems on sleeves.

• Tech Pack Tip: Edge finishing is a massive indicator of garment quality. A luxury tech pack might specify a bound interior edge (Class 3) instead of a basic overlock (Class 6) for a cleaner, higher-end finish.

Class 7 – Attaching Separate Items

• What it is: A seam that attaches a completely separate, often non-fabric component (or an extended trim) to the edge of a garment piece. The attached item usually extends past the fabric edge.

• Common Applications: Attaching elastic bands to the waistline of underwear, sewing rigid lace trim onto a hem, or attaching a woven binding braid.

• Tech Pack Tip: Because you are often joining two materials with completely different properties (like rigid lace to a stretchy knit body), your tech pack can specify the correct machine folder required and tension tolerances so the factory doesn't warp or stretch the fabric while attaching the trim.

Class 8 – Single-Ply Construction

• What it is: A seam created using only one single piece of fabric that is folded in on both of its outer edges and stitched together to create a continuous strap, tube, or band.

• Common Applications: Belt loops on jeans, fabric waist belts, and spaghetti straps on dresses.

• Tech Pack Tip: Factories use a specialized machine attachment (called a folder) to feed this single ply of fabric evenly through the machine so both edges fold perfectly. You must specify the exact finished width of the strap so they know which specific folder to attach to the sewing machine.

Common Seams Used in Apparel & Accessories

Beyond classification, here are practical seam types frequently used in production.

Felled Seam

ABC Seams

• Resistant, flexible, durable

• Suitable for woven and knit fabrics

• Works on straight and curved seams

• Inexpensive

This seam conceals raw edges by folding them under and stitching with two rows. It’s commonly seen in denim and workwear.

Best for: Durable garments requiring strength.

Bound Seam

ABC Seams

• Strong and resistant

• Decorative binding finish

• Best for medium-weight fabrics

Binding encloses the raw seam edge for a clean interior look.

Welt Seam

ABC Seams

• Strong, durable

• Clean, high-end interior finish

• Best for lightweight fabrics

Often used in tailored garments.

Lapped Seam

ABC Seams

• Excellent flexibility

• Good elongation recovery

• Reduces bulk in heavy fabrics

Useful in performance and outerwear applications.

Sandwich Seam

ABC Seams

• Excellent resistance

• Flexible with strong recovery

• Reversible finish

Suitable for a wide variety of fabrics.

Specialty Seams You Should Know

French Seam

ABC Seams

A seam within a seam. The fabric is stitched wrong sides together first, then folded and stitched again to fully enclose raw edges.

Best for:

• Sheer fabrics

• Lightweight garments

• Clean interior finishes

Flat Felled Seam (Single Needle)

Itch to Stitch

• Two rows of stitching

• Concealed raw edges

• Very strong

Common in jeans and workwear.

Taped Seam

Pinterest

Tape is applied over a seam to:

• Reinforce

• Reduce stretch

• Add waterproofing

Common in sportswear and outerwear.

Butt Seam

Pinterest

Edges meet without overlap and are stitched using coverstitch machinery.

Best for:

• Underwear

• Performance knits

• Low-bulk construction

Hems & Edge Finishes

Hems fall under edge finishing (Class 6).

H110 – Fold Hem

ABC Seams

• Most popular hem for wovens

• Durable and neat finish

• Suitable for most fabrics

H101 – Bound Hem

ABC Seams

• Very strong

• Prevents ravelling

• Adds decorative weight

H200 – Bound Edge

ABC Seams

• Reinforces and protects edges

• Decorative and functional

H000 – Unhemmed Edge

ABC Seams

• Low cost

• Flexible

• Used in casual or raw-edge designs

Structural Details That Affect Seams

D110 – Pleat

ABC Seams

Adds volume and flexibility. Often reversible.

D210 – Patch

ABC Seams

Adds strength and reinforcement to high-stress areas.

Seam Quality: What Brands Should Monitor

Seam performance can be evaluated by:

1. Seam Strength

• What it is: The amount of physical force or tension a seam can withstand before it either rips open or the thread snaps.

• Why it matters: If your seam strength is lower than the strength of the fabric itself, the garment will fall apart under normal wear and tear.

• How to control it: Seam strength is determined by three things: the type of thread used (e.g., polyester core-spun vs. cotton), the Stitches Per Inch (SPI), and the seam type. Heavy-duty garments like jeans require high-strength construction like a Felled Seam paired with a thick thread and a dense SPI.

2. Seam Slippage

• What it is: This happens when the actual thread doesn't break, but the yarns of the woven fabric pull away from the stitching under tension, creating a visible gap, laddering, or a hole right next to the seam.

• Why it matters: This is a massive quality control issue, especially common in loosely woven fabrics, smooth synthetics, or delicate silks. It makes a garment look cheap and damaged instantly.

• How to prevent it: If you are using a slippery or loose fabric, you can prevent slippage by increasing the seam allowance, using a French Seam to trap the raw edges, or applying a lightweight fusible interfacing along the seam line to reinforce the yarns.

3. Seam Width and Depth (Seam Allowance)

• What it is: This refers to the distance between the raw edge of the fabric and the actual line of stitching (often called the seam allowance).

• Why it matters: If the seam width is too narrow, the fabric will fray, and the seam will blow out. If it is too wide, the seam will feel stiff, bulky, and alter how the garment drapes on the body.

• How to control it: Standard internal seams usually have a 3/8" or 1/2" width, while tailored garments might use up to 1" so the customer can alter it later. Your tech pack and digital patterns must state the exact seam width so the factory knows where to align the fabric under the needle.

4. Bulk and Comfort

• What it is: The physical thickness and stiffness of a seam when multiple layers of fabric are folded and stitched together.

• Why it matters: Excessive bulk destroys comfort. If you have a bulky seam at the armhole or inner thigh, it will cause severe chafing. Bulk also ruins the aesthetic of a garment by creating weird, lumpy ridges that show through to the outside.

• How to fix it: Technical designers reduce bulk by "grading" the seams (trimming the hidden layers of fabric to different widths), pressing seams flat and open, or using a Lapped Seam (which reduces the number of fabric layers stacked on top of each other).

5. Stretch and Recovery

• What it is: * Stretch is the seam's ability to elongate at the exact same rate as the fabric when pulled.

• Recovery is the seam's ability to snap back to its original length without the stitches popping or staying stretched out (often called "bagging out").

• Why it matters: If you sew a highly stretchy knit fabric (like yoga pants) with a rigid, non-stretch straight stitch, the thread will snap the second the customer pulls the pants over their hips.

• How to control it: For activewear, swimwear, and knits, you must specify stretch-friendly stitches in your tech pack, such as an overlock, coverstitch, or zigzag stitch. You also need to specify "looper" threads (like Woolly Nylon) that naturally stretch with the garment.

Why Seam Selection Matters in Product Development

Seam choice impacts:

• Durability

• Fit and comfort

• Production cost

• Bulk

• Fabric compatibility

• Garment longevity

Using the wrong seam can:

• Increase production costs

• Cause seam failure

• Lead to return issues

• Complicate sewing

This is why seam specifications must be clearly documented in your tech pack.

Conclusion

Seams are far more than just aesthetic stitching details; they are fundamental structural decisions that dictate a garment's quality and lifespan. A solid understanding of different seam types allow you to engineer stronger, higher-performing garments while strategically reducing fabric bulk in critical areas for maximum comfort. Ultimately, mastering these constructions empowers you to communicate your technical requirements clearly to your manufacturing partners, ensuring a flawless finish and preventing costly production errors before they happen.

In garment construction, seams are where design meets engineering. Choosing the right seam type is only useful if it’s clearly documented and communicated to your manufacturer.

At Tech Packs Co, we help brands translate design intent into production-ready tech packs—including seam construction, stitch types, finishes, and material specifications. Strong garments start with clear construction. Book a consultation with us and build with precision.

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