DIY Tarp Ridgeline - Grosgrain or none?

[BackpackerGuy]

This is similar to how Warbonnet makes his ridgeline (although I think he uses polyester bias tape instead of grosgrain).

All of the bias tape I find at the fabric stores are a combinational of polyester and cotton.
I'm leery of the cotton content.
Won't it absorb and hold moisture?
If so, this could lead to rotting.
Is there a source for 100% polyester bias tape somewhere?

[turnerminator]

I don't understand either. I have 3 WB tarps and was told I didn't need to seal the ridge lines. They all turned light rains with no problem.
On one campout it rained steady for 6 hours strait. The ridge lines on all three tarps started leaking after about an hour. The next 5 hours were miserable. The leaks weren't limited to a spot here or there - they leaked along the entire ridge line (all three of them).
Guess what I did the next weekend?

I've seen this too. Not a problem until the heavens open.

It was running through the stitch lines-my friend spent the next 7 days with a plastic sheet over the hammock to stop the leaky ridge from saturating his gear in the night.

[gmcttr]

All of the bias tape...

Bias tape, that I'm familiar with, is made to stretch and is used to edge sleeves and collars, so I doubt that is what you want (even though some report it being used by cottage vendors).

I believe grosgrain is more commonly used.