Here’s an example why it’s so very important to use quality marine grade materials. This is a V-Birth cushion that had been re-upholstered by another shop 8 years ago. The fabricator did not use a quality marine zipper. You can see the results. The zipper was unusable and the cover had to be cut off the foam.
To make matters worse, the foam was completely wrapped in a heavy poly plastic sheet. We typically wrap the foam so it can be vacuumed and shrunk while fitting the cover. However, I would never use plastic this heavy. The plastic was very noticeable when sitting on the cushion, enough so that it made it uncomfortable. It also retained moisture and didn’t let the foam breath. The foam was waterlogged, covered in mildew and made the V-Birth smell awful. The cover and foam both had to be replaced.
Look, we all know that having the word “marine” on the package almost always means you’re paying quite a bit more. The extra investment is often worth it. And when it comes to canvas, cushions and upholstery, it’s always worth it. This cushion would have had many years more service had it been done with Nautolex marine vinyl, a quality YKK Vislon or Coil zipper and Solarfix lifetime thread. The longevity of quality built canvas projects far out-value the savings you might see from accepting cheaper materials.