synthetic insulation “Topper” for Sleeping System.

2.5 Apex is what I would use.

Do NOT, however, use Silnylon. It will exasperate precisely what you are trying to avoid – a wet down bag. Use M50, Nobul, M90, 1.1, or other light, non waterproof fabric.

Since the sil is waterproof the moisture will stop where sil touches your down bag. You know how that will end up.

As for the noise – I've used a "topbag" over my quilt and didn't notice any noise at all aside from the slight brushing sound when I roll over. Shouldn't be an issue.

Please show us what you end up with!

Thanks Todd. Yes, definitely I need breathable fabrics for this application. I think I may go with Nobul. I'm new to sewing so hopefully not too difficult to work with.

Cheers.

edit: spelling

I've done nobul1/synthetic. Works good.

When I sewed through nobul1/synthetic/some other fabric, it was hard to keep them all aligned. One would slide relative to the others.

When you lay it out and cut it, you should generate some long skinny pieces. Use those to practice. Cut strips of nobul/synthetic/nobul that are the same length. Sew a line of stitches. You will probably find by the end of the line of stitches that the three pieces are no longer aligned, one will stick out longer.