Twill tape is a type of fabric tape that is woven in a twill pattern, meaning that it has parallel diagonal ribs. This woven pattern is extremely sturdy, making the tape a very popular sewing notion; twill itself has been woven for centuries. Most sewing stores carry this tape, typically in an assortment of colors, weight grades, and widths, to satisfy a range of sewing needs. It is also possible to order it directly from manufacturers; this is advised if you have a major project and you want a cheap bulk rate.
There are all sorts of uses for twill tape. It is often used, for example, to make sturdy ties on things like hospital gowns. It can also be integrated into seams to reinforce them, or used for trim. Many sewers use it to make tags, since the tape will hold up through years of use without being scratchy, and some conservators use the tape to label things like ancient textiles, since the tape will not react with the materials used in the textile.
A variety of materials can be used to make twill tape. Cotton tape is very common, as is polyester, but wool, linen, and even silk may be used in some regions. Many companies make “naked” tape, meaning that it is undyed, while others produce a range of colors and sometimes patterns as well. Widths typically vary, allowing people to use very slender varieties for projects like ties, and wider ones to reinforce heavy seams and the like. Most company also make lightweight and heavy duty twill tape for specific tasks.
Depending on the material used to make twill tape, it can often easily be dyed another color. People can also paint or stencil patterns onto the tape, along with other information such as a catalog number or a seamstress' name. In some regions, people also embroider the tape, as it holds embroidery very well. The sturdy weave also resists distortion, ensuring that patterns remain true to their designer's wishes.
The quality of twill tape can vary, with especially cheap tapes being prone to raveling and running dyes. If you aren't sure about the quality of a piece, you may want to test a sample for colorfastness before you throw it in the wash, as running colors can stain garments. It also helps to tightly sew down the ends of a strip of it to reduce raveling.