Interlining

Interlining is a layer of fabric inserted between the face and the lining of a garment, drapery, or quilt. It is similar to batting, a thick layer of fiber designed to provide insulation, loft, and body to quilts, pillow toppers, and heavy winter jackets. Depending on the application, the materials in this layer can be woven, knitted, or created by fusing fibers together. Silk, wool, and artificial fibers with good insulating qualities are common choices for interlining.

Generally, interlinings are soft, thick, and flexible. Some are designed to be fused, while others are intended to be sewn to one or both layers of the textile. As an inner lining within textiles, it is used in a number of applications. Though the consumer never sees it, it is the difference between a good winter coat and a great one, or lush full drapes and listless hanging fabrics.

In many cases, interlining serves as an additional layer of insulation. For example, drapes are often interlined with flannel or a similarly thick material to keep rooms warmer in winter and cooler in summer, while many winter coats and pants use a thick layer to protect the wearer from the elements. Some of these garments also feature removable interlinings, so that they can be worn in warmer weather as well. Interlining can also be used to protect fabrics, especially those used in drapes and consequently often exposed to direct light. Delicate fabrics like silk and velvet can suffer from sun damage if hung with a liner alone, and most drapers recommend the use of an interlining for the life of the fabric. In addition to protecting the fabric, it also gives drapes a better form and fuller body. In quilting, the layer can offer an extra bit of fluffiness, along with warmth in the winter.

Garments with interlining tend to be stronger, because of the added layer of fabric support. In addition, they drape better, while keeping the wearer's temperature relatively stable. Interlining generally bespeaks a higher level of quality in a garment, because of the additional manufacturing time involved.

SPI Recommendations for Woven & Knits

A list of garments and the typical number of Stitches per Inch recommended for each of them is given below:

WOVEN GARMENTS

Garments	SPI	Comments	Garments	SPI	Comments
Denim Jeans, Jackets, Skirts	7 – 8	Fewer stitches per inch Generally will give a more contrast stitch appearance.	Children’s wear	8 - 10	Usually 8 to 10 SPI is adequate to provide adequate seam strength and at the same time allow for quicker cycle Times.
Twill Pants or Shorts	8 – 10	More stitches per inch Will help minimize seam grinning.	Dresses, Skirts	10-12	Due to many of the operations being lockstitch, usually 10 – 12 SPI is required to provide adequate seam Strength.
Trousers, Dress Pants, Slacks	10-12	On some operations like serge panels, it may be desirable to use a longer stitch length.	Blind-stitch Operations on Slacks, Dresses Skirts, etc.	3-5	A long stitch length is desirable to minimize the dimple or appearance of the needle penetration on The outside of the garment.
Dress Shirt or Blouse	14-20	Using more SPI allows the use of smaller diameter threads that will minimize seam Puckering.	Button-sew (4 hole button)	16	Button-sew machines are cycle machines with a predetermined number of stitches per cycle.
Casual Shirts, Blouses, Tops	10-14	Using more SPI will give more of a tailored stitch Appearance and better seam coverage when surging.	Buttonhole (1/2” purl or whip stitch)	85-90	Generally sewn vertically – approx. 85- 90 stitches with a lockstitch buttonhole Machine.

When setting standards for stitches per inch, you should always keep in mind that more stitches per inch used in a seam requires longer sewing cycles to complete the seam. Longer sewing cycles translates in to higher labor costs and lower production levels. Sewing machine sewing at 5,000 SPM (stitches per minute) at 8 SPI will sew 17.4 yards of seam per minute. Sewing machine sewing at 5,000 SPM at 14 SPI will sew 9.9 yards of seam per minute.

More stitches per inch will also consume for thread per inch of seam. This will contribute to higher seam strength and more elastic seams, but will also increase the consumption of thread required to sew the garment.

Therefore, the recommendations listed above are common stitch levels that provide adequate seam strength but also take into consideration the factors just mentioned.

When sewing knit fabrics, you should always check for excessive “seam grinning” of the seam; and also check for “stitch cracking”. “Seam grinning” occurs when thread stitch balance is too loose allowing the seam to open up too much when stress is applied to it. “Stitch cracking” is checked by applying pressure on the seam in the stitching direction. If the thread tensions are too tight or if you are not using enough stitches per inch, the threads will rupture as stress is applied on the seam. Therefore, the following recommendations have been made for the number of stitches per inch to be used on the following garments.

KNIT GARMENTS

Garments	SPI	Comments	Garments	SPI	Comments
Jersey T-shirts, Tops, Polos	10-12	Using more SPI increases the chance of needle cutting.	Swimwear	12 - 16	The more elastic the seam, the more SPI that should be used to minimize stitch cracking.
Underwear	12-14	The more elastic the seam, the more SPI that should be used to minimize stitch cracking.	Dresses, Skirts	10 - 12	The more elastic the seam, the more SPI that should be used to minimize stitch cracking.
In fantwear	10-12	The more elastic the seam, the more SPI that should be used to minimize stitch cracking.	Intimates	12 -16	The more elastic the seam, the more SPI that should be used to minimize stitch cracking.
Fleece	10-12	More stitches per inch are required to provide the proper seam coverage on fleece.	Stretch Knits (Lycra®, Spandex®, etc.)	14-18	More stitches per inch are required to provide the proper seam coverage on fleece.
Sweaters (Med. To Heavy.)	8-10	The more elastic the seam, the more SPI that should be used to minimize stitch cracking.	Hosiery, Socks	35-50	Usually sewn with very fine thread. More spi are required to minimize seam grinning and seam elasticity.

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