Heat-Seal Fabrics

Hot Topic

What are heat-seal fabrics? Heat seal is a general term for woven fabrics with a heat-sensitive substance laminated to or coated on the fabric wrong side. Nylon is the fiber most frequently used because of its high strength and water resistance. The heat-sensitive laminate allows seams to be constructed with or without stitching. These fabrics are available in a variety of weights and fabric types. Heavier weights for rugged apparel and outdoor gear include pack cloth and ballistic nylons. Many suppliers list a denier number with each fabric name. Denier is a term describing yarn size. The higher the denier number, the larger the yarn and, therefore, the heavier and sturdier the fabric.

Terminology

Heat-seal properties are created by either laminating or coating.

Laminated fabrics have a heat-sensitive substance applied to the fabric wrong side. The fabric face appears unchanged while the back is smooth and slippery. Laminated fabrics still may be torn on the grain line and can be stitched in the same manner as the fabric without the laminate.

Coated fabrics have heat-sensitive substances applied to one or both fabric sides. When coating is applied to both sides, the fabric feels more like a vinyl sheet and can no longer be torn or stitched in the same manner. Potential for confusion exists because the words laminated and coating sometimes are used interchangeably. The information discussed in this article will apply to fabrics with heat-seal substances on one side only.

When properly constructed, these fabrics offer airtight, waterproof qualities. The fabrics may be sewn with conventional seams or constructed entirely by heat-sealing; a combination of techniques is helpful for some projects. While some heat-seal fabrics require an electronic weld to hold fabric layers together, fabrics available to home sewers may be heat-sealed with a standard iron. (See "Sources" at the end of this article).

Project Selection

Because seams must be handled differently for heat-sealing, projects with few seams are ideal. Keep in mind these fabrics don't "breathe," so they aren't suitable for garments worn next to the skin for long periods of time. They're great, however, for storm-proof garments and outdoor equipment. Use them to make ponchos, raincoats, hats, simple tents, shelters, camp mattresses, cushions and bags, book bags, lunch bags, tote bags, camping bags, dry bags for river rafting or kayaking and more.

Getting Started

Use an old iron. The laminate may be impossible to remove if it comes in contact with the iron.
• Place a protective cover on the ironing board, but avoid using covers with napped or raised surfaces. Textures may be permanently pressed into the fabric when heat is applied.
• Use smooth press cloths and pressing paper. A press cloth over the fabric protects the fabric from melting or scorching and prevents the laminate from damaging the iron.
• Check the fabric for colorfastness by soaking a small swatch in hot water. Some brightly colored fabrics may bleed when first exposed to water.
• No preshrinking is necessary. The fabric is stabilized by the laminating process and won't shrink.
• Test the fabric to determine the laminated side before beginning. The shinier fabric side usually is the laminated side, but it's more obvious on some fabrics than others.

Fusing Heat-Seal Seams

• Use a hot iron to seal seams. It's necessary to use a cotton or linen setting on most irons, but experiment to find the best temperature for your iron. The use of a heavy press cloth also will require a higher iron temperature.
• Heat-seal seams with the laminated sides of the fabric together, producing seam allowances on the outside. For equipment and outdoor gear, this isn't a problem. For apparel, you can stitch and seal the seam allowance as instructed in "Stitching Heat-seal Seams" later in this article, or pink the edges to create a whimsical appearance.
• With the press cloth over the fabric, press the iron down for approximately 15 seconds, then lift; don't slide the iron. Let the fabric cool before handling. Check the seal. If the fabric can be pulled apart, press again, holding the iron in place for a longer time period. A successfully sealed seam is almost impossible to pull apart when cool.
• When heat-sealing a seam, the heat must be applied only in the seam area. This can be tricky because the seam area is hidden from view by the press cloth. Remember, the fabric will seal anywhere heat is applied. Any narrow surface that raises the area to be sealed and allows the rest of the fabric to fall away from the pressing area is an indispensable aide. (A standard seam roll doesn't raise the seam area enough.) A magazine with a smooth binding the width of a seam allowance can be spread open, face down, and used as the raised area. Place a press cloth over the magazine, position the seam on the binding and press only on the raised area.

• Seams also may be stitched in the conventional manner. The fabric weight will determine the needle size. Use a new needle with a sharp point to prevent snagging or distorting the fabric.
• If stitched seams must be waterproof or airtight, you can seal them with seam-sealing products such as McNett Aqua Seal™, Sil-Net Seam Sealer™ and Plastiseam®. Flat-felled and overlapped seams are the easiest to seal after stitching.
• An easy alternative method is achieved by sealing heat-seal fabric strips over the seams wrong side. After stitching a conventional seam right sides together, trim one seam allowance to 1/4". Trim the other seam allowance to 3/8" and finger-press both seam allowances to one side. Cut a 3/4"-wide heat-seal fabric strip and place it along the seamline on the garment's wrong side with laminated sides together. When heat-sealed in place, the seam should be waterproof and have a finished look on the garment inside.

Seattle Fabrics, Inc., (206) 525-0670; fax (206)525-0779. www.seattlefabrics.com Dry bag instructions are available free with the purchase of heat-seal fabric.

The Rain Shed, Inc., (541) 753-8900 www.therainshed.com

Outdoor Wilderness Fabrics, Inc., (208)-466-1602 or (orders only) (800) OWF-SHOP (693-7467); www.owfinc.com

Subscribe More Articles Past Issues