Technical

5 Things Engineers Should Know About Working with Fabric

Soft Goods: Hard Development

Are you working on a wearables project? Struggling to understand the world of fabrics and how to incorporate them into your design? I’m here to iron out your confusion and get you started on the right thread.

1. There are two general categories of fabrics: knits and wovens.

What is a knit? Think T-shirt fabric. It is constructed from one long thread that is looped through itself to form a sheet. By its nature, it forms a stretchy material because the loops can change shape under force. The fibers themselves are usually not elastic. Knits can be stretchy in one axis (called 2-way stretch) or in both axes (called 4-way stretch).

The green thread is looped through the preceding and subsequent loop rows, forming a snaking pattern

The green thread is looped through the preceding and subsequent loop rows, forming a snaking pattern

 

Woven fabric is constructed by weaving threads back and forth in one direction (weft) alternating over and under threads running perpendicular to them (warp). The point at which the warp threads turn around is called the selvage and is the edge of the fabric that does not fray. Woven fabric is generally not stretchy unless the fibers themselves are elastic. If you need some stretch in your woven fabric look for a fiber blend that contains a percentage of spandex (an elastic fiber).

The pink threads are the long weft threads. The blue thread alternates over and under weft threads to form the fabric.

The pink threads are the long weft threads. The blue thread alternates over and under weft threads to form the fabric.

2. Woven fabric has different properties based on the orientation in which you cut your piece.

The best way to understand this is to take a square piece of fabric (like a handkerchief) and grab one corner with one hand. Grab each of the other corners in turn and give a gentle tug. You will notice that when you are grabbing diagonal corners, the fabric stretches even though it has little stretch in the other orientations. 

The imaginary bias line runs 45 degrees to both warp and weft threads

The imaginary bias line runs 45 degrees to both warp and weft threads

 

Because of the construction of woven fabric the diagonal direction (called bias) is stretchy. This is why home sewing patterns specify the orientation you lay your pieces out to cut when making a garment.

3. Stretch fabrics and non-stretch fabric should be seamed differently.

If you’re wearing a t-shirt, take a look at the inside seams. Compare with someone wearing a dress shirt. You will probably notice that t-shirt stitching looks different. It’s probably serged, which is a different process than traditional sewing requiring 3 to 4 threads and a different machine than a standard sewing machine.  

fabrics4

Sergers (pictured on the right) require 3 or 4 threads and form a stitch that locks around the outside edge of the fabric. A standard home sewing machine (pictured on the left) requires two threads (a top spool and bobbin). Home sewing machines can do straight, zig-zag and a variety of other stitch patterns.

Straight stitches in white on the left, Serged edge in grey on the right.

Straight stitches in white on the left, Serged edge in grey on the right.

 

A serger cuts and binds the edges as it goes and can be used with stretch or non-stretch fabrics because the looping pattern can extend as needed.

If you’re prototyping and don’t have a serger, don’t use a straight stitch on your stretch fabric. Straight stitches don’t stretch, and your seams will fight the stretch. Instead, switch to a zig zag. You will get much better results.

4. Soft goods product requirements have to be communicated differently from hardware product requirements.

Communicating with soft goods manufacturers (like communicating with any manufacturer) can be difficult. Unfortunately, soft goods (generally) don’t have the language of CAD to communicate. The garment industry uses what is called a “Tech Pack” to communicate with the manufacturing team about a product. This includes items such as technical flats (think engineering drawing for clothes), material and color samples (usually called swatches), fashion sketches (think industrial design rendering), paper patterns and physical samples.

In my experience, while all these things are useful, physical samples and material samples are by far the most useful. I have been amazed at factories’ abilities to copy a sample. They can find a similar fabric that they can consistently source and then after they own the pattern and design, you can trade samples with them, making modifications on the samples and then sending updated versions back and forth until you have the design dialed in.

5. There are options other than traditional cut and sew manufacturing techniques.

Many wearable and other fabric products (including sportswear garments) are now made with heat set adhesives. When used properly they can be amazingly effective. At the same time know the limits of what you’re working with. A few general things to keep in mind:

  • Machines: heat set adhesives require different machines. If you need to do both sew and adhere your product you might need to find two factories or spec a factory that has both processes in house.
  • Process: To get good results using adhesives you need a correctly dialed in procedure of heating, pressing and cooling. This should be based on the heat set adhesive’s specific properties and can be difficult to get right. In contrast, sewing is such a common and well understood manufacturing technique that factories should have no trouble getting it right.

I could write a lot more about heat set adhesives but for now, you can learn more by checking out some of the heat set adhesive supplier’s websites:

I hope these tips have patched some holes in your knowledge about textile manufacturing and product development. By heeding this advice you should be able to keep your next soft goods project from unraveling.