Within the marine canvas and upholstery world, there are two main kinds of thread used, bonded Dacron/polyester and PTFE (Polytetrafluoroethylene), which is more or less Teflon®. We feel that both threads have their place in our shop.
The Dacron or polyester thread is the most commonly used thread in our industry because of its strength to exposure life ration. A nylon thread would be much stronger but would burn up much faster in the sun, making it a poor choice for use on a boat. Many Dacron thread manufactures also incorporate an anti-wick property, which means that as the thread gets wet it expands filling the hole helping to keep the water from getting through. For our Snap Covers, Cinch Covers and FCT‘s we fill this is the best thread for the application due to the actual exposure these covers should see.
PTFE thread is our go to, never going to fail due to exposure, thread. For our Storage Covers or ANY work, we do at Lake Powell, Flaming Gorge or Bear Lake we always use PTFE. PTFE will not fail due to sun exposure, salt, chemicals or pollution in the air. With its warranty of outlasting any fabric, you put it in comes to a higher price, and I would say that 9 times out of 10 it is worth the added expense.