# Dropstitch Inflatable Fabric

Dropstitch Inflatable Fabric (also known as double wall fabric, three-dimensional fabric, distance fabric, or drop stitch inflatable fabric) is a textile product composed of two layers of woven fabric connected by threads, referred to as drop yarns or drop stitch threads. When the fabric layers are coated with an airtight material, typically TPU or PVC, the structure becomes inflatable and capable of holding its shape under pressure. The inflated pockets created by the drop yarns provide the fabric with structural rigidity, enabling the creation of flat-sided, pressure-resistant structures.

## History

The origins of drop stitch technology can be traced back to the 1950s, when Goodyear developed a process similar to velvet manufacturing, initially calling it "Airmat". This technology was initially employed in the construction of inflatable airplanes. Early drop stitch fabrics faced limitations in thickness, reaching a maximum of approximately six inches. Creating specific shapes required cutting and sewing the fabric, a process that was expensive, time-consuming, and often resulted in inconsistent shapes. A significant advancement came with Earl Bilsky's patent in 1966, assigned to Goodyear Aerospace Corporation, which detailed a method for weaving contoured drop stitch inflatable fabric. This method involved extending the drop yarns to predetermined lengths during weaving, resulting in precise inflatable shapes without the need for cutting and sewing. While Bilsky's patent mentioned wire yarns, drop stitch can be manufactured using various materials, including nylon, rayon, and other natural or synthetic fibers. Dropstitch was used in the creation of gymnastic mats before its widespread use in standup paddleboards.

## Manufacturing

The manufacturing of drop stitch fabric involves weaving two layers of fabric in parallel on specialized machines that use hundreds of needles, sometimes exceeding 400. These machines can produce drop stitch fabrics in widths ranging from 5 to 10 feet. Adjusting the spacing between the fabric layers during manufacturing is a complex and time-consuming process, often requiring up to 20 days to modify the needle setup. After the weaving process, an airtight coating, typically TPU or PVC, is applied to both surfaces of the fabric. Two common methods for joining drop stitch components are gluing and welding.

## Properties and Applications

Drop stitch inflatable fabrics exhibit several advantageous properties, including:
* Structural rigidity: The interconnected fabric layers and inflated pockets create a rigid structure capable of supporting weight and maintaining shape
* Flat sides: The presence of drop yarns allows for the creation of flat surfaces, unlike traditional inflatable structures that tend to form cylindrical shapes
* Pressure resistance: Drop stitch fabrics can withstand high internal pressures, typically up to 20 psi, making them suitable for various demanding applications
* Lightweight and Portable: The use of lightweight fabrics and the ability to deflate and fold the structures make drop stitch products highly portable
The rigidity of drop stitch fabrics is influenced by the internal pressure and increases with higher pressures. Another major advantage of drop stitch technology is its ability to create unique shapes that would be difficult to achieve with simple inflatables.
These properties have led to the widespread use of drop stitch fabrics in a diverse range of applications, including:
* Recreational equipment: Stand up paddleboards (SUPs), eFoils, boats, kayaks
* Sporting goods: Air mats for gymnastics
* Outdoor and shelter: Tents, inflatable shelters, emergency housing
* Industrial and construction: Concrete houses, formwork for concrete structures
* Other: Pools, plunge tanks