I not an expert but I have owned a small manufacturing company in the past. And based on my limited experience here is how I would approach your project.
You first need to figure out what your goals are for this project. What exactly is your business objective? Is it to produce and sell the Bentley of electrician belts on the market and differentiate by only using the very best materials on the planet? Is the goal to be the most affordable belt on the market? What is your value proposition and how will you stand out from the competition? The answer will determine how you get your product made. If you want the Bentley of belts, you might be looking at a hand made operation based in the US and if it's the cheapest priced belt, you're probably looking at a certain type of manufacturer in China to outsource the belts to.
The next step I would take, depending on what type of market you will be competing in, is to determine whether or not you should be using a private labeled product. A private labeled product is a product that you order from a manufacturer who already makes that product but with your company logo on the product labels and packaging. This is how most products are made because it's the most economical choice due to economies of scale. If someone is already making that product, they will have more experience and they can combine buying power of the raw materials to bring the prices down even more.
There are certain types of products that work the best with private labeling. For example, private labeled products work well with products like a toilet bowl brush or shower curtain or clothes hanger because people don't care about the brand as much as they care about the brand for a product like a TV or an audio system for your home theater or living room. When purchasing an audio system people care a great deal about the brand. Whether the brand is Samsung, Toshiba, Sharp, Sony. JVC, Pioneer, Denon, Yamaha, or Harman Kardon, the brand makes a big difference in how the product and price is perceived by the consumer. I have no idea if the brand makes a difference for Electrician belts or what type of market position is the most profitable so you'll have to do your homework.
If you want to be the Bentley of belts and make a completely different design, you have less of chance going the private label route but it's not impossible for the design to be changed so you'll just need to find the comparable type of manufacturing company that can make a product at the quality level you expect.
If you don't go the private label route, your job will be to set up your own manufacturing operation and you'll need to hire a textile engineer to help you with material selection and a VP of manufacturing with the relevant experience to oversee the entire operation.
If selecting the materials is your only concern, you can hire a boutique consulting company that provides this type of service and their consultants will be ex textiles engineers etc. Or you can find retired people who used to work in that role. Or someone who changed industries recently. The reason for this is because people who are currently employed as textiles engineers for an employer is probably working under an NDA that prohibits them from giving out trade secrets or any sensitive information for obvious reasons, competitors etc.
After you determine the materials, you can ask the private label companies to use those materials. Personally, I would simply use what everyone else is using because you don't know what you don't know and there is usually a good reason 80% of the competitors are using the same material. And that reason might not be immediately apparent to you which might cause headaches down the line.