Silpoly and condensation

[joe_guilbeau]

My experience with nylon and polyester and some thoughts on rainy conditions with an attached video.

Rain test comparison of nylon and polyester fabrics. Two similar tents whose flysheets are both constructed of 30 Denier 300T with siliconized application to both sides of the flysheets.

Denier is used to specify the thickness and strength of fabrics. A single strand of silk is where the standard’s baseline is established and is 1-Denier.

The 300T is the sum of vertical and horizontal threads per square inch.

The higher the denier count, the greater the diameter of the fabric’s strands. Different fabrics have differing reactions to water. Nylon absorbs more water than polyester.

HydroTex Siliconized Polyester used in the tent in the foreground of the video is composed of fabric compared to Nylon in Rain Test

Same manufacturer, same tent design, same color of fabric. The only difference between the tents is the fabric being used.

Now, the pro’s and con’s are that the polyester tent does not absorb as much water as the nylon tent, and therefore sags less.

If both tents were deployed using only flysheets, then condensation will degrade the performance of the polyester tent to a greater extent than that of the nylon tent.

The reason is that the nylon tent will absorb more interior condensation and therefore there will be less water droplets forming above one’s head.

The polyester tent will not absorb as much water, therefore there will be more condensation formed on the overhead portions of the flysheet, and any wind in the morning will shake the condensation loose and wet anything lying below.

This becomes important in tarp usage. A steeper pitch (think A-Frame) will be required in high condensation conditions for the polyester tarp, to allow the droplets to form and roll down the fabric.

A polyester tarp can ‘batted’ to shake off more of the droplets that have formed to the ground and the polyester fabric will dry faster than the nylon material.

Here is a video that highlights the differing reactions of both materials under similar conditions.

[deadeye]

In those conditions, without a breeze to move the moisture away, you're going to get condensation regardless of tarp material. Opening up the tarp, think porch mode, can help some.

I agree with this - condensation/frost will form under any material, waterproof or not, under the right circumstances. When I ski, I wear a breathable windshirt (not waterproof or even DWR) over a fleece, and will get frost inside. When I hang a tarp in fall before the ground freezes, I'll get frost inside the tarp even if I'm not sleeping under it.

It's just one of those things you have to deal with.