Silnylon at a glance
- Typical shelter
- 15D to 30D
- Stretch when wet
- Noticeable
- Silpoly barely moves
- Seam sealing
- Usually DIY silicone
- Price vs DCF
- About a third
Why it sags
Nylon absorbs a small amount of water into the fiber itself, and when it does the fiber swells and lengthens. On a pitched shelter that shows up as a canopy that was drum tight at dusk and slack by midnight, and it is a property of the nylon rather than a fault in the pitch.
The usual answers are to pitch it slightly tighter than feels right, to leave a little adjustment in the guylines so you can take up slack without getting out, or to buy silpoly instead. Polyester barely absorbs water, so a silpoly shelter holds its pitch. It is slightly heavier for the same strength and has become the default on a lot of shelters for exactly this reason.
Silicone means you have to seal it yourself
Standard seam tape does not stick to silicone, so silnylon seams are sealed with a silicone sealant thinned with mineral spirits and painted on, rather than heat-taped at the factory. Plenty of shelters ship unsealed with a tube in the box, and a first-trip leak along the ridgeline is almost always this.
A polyurethane-coated fabric is the opposite: tape bonds to PU, so those shelters arrive factory sealed. It is one of the practical trade-offs between the two coatings, alongside PU being heavier and hydrolysing with age.
What this means when you're choosing
- Whether it is silnylon or silpoly, since only one of them holds its pitch overnight
- Whether seams arrive sealed, because silicone cannot be factory taped
- The denier, which is what actually decides durability
- Adjustable line locks on guylines so you can retension without getting up
Silnylon vs Dyneema Composite Fabric
| Silnylon | Dyneema Composite Fabric | |
|---|---|---|
| Sag when wet | Noticeable. Expect to retension overnight | None. Pitch it once |
| Price | The affordable default | Two to three times more |
| Handling | Stuffs and packs without much care | Roll it. Repeated hard creases degrade the laminate |
| Weight | Heavier, though not by as much as people assume | The lightest option in common use |
Which to pick: Silnylon for most people and anyone hard on gear. DCF if you pitch in the wet often enough that never retensioning is worth the money.
The common mistake
Blaming a sagging pitch on your technique
A silnylon canopy that goes slack a few hours after you pitch it is doing what the fabric does when it takes on moisture. Pitch a touch tighter, leave adjustment in the lines, and stop trying to solve it with stake placement.
Common questions
Why does my silnylon tent sag at night?
Nylon absorbs moisture and the fibers lengthen, so the canopy relaxes as humidity rises. Pitch it slightly tighter than feels necessary and leave adjustment in the guylines. Silpoly shelters do not do this.
Is silpoly better than silnylon?
For holding a pitch, clearly. Polyester barely absorbs water so it stays where you put it and it degrades less in UV. Nylon is stronger for its weight, so silnylon is still chosen where weight is the priority.
Do I have to seam seal silnylon myself?
Usually. Tape will not bond to silicone, so these shelters are sealed with a thinned silicone sealant painted along the seams. Many ship unsealed with the tube included.
Where this is defined
- ISO 811 hydrostatic pressure test for fabrics, International Organization for Standardization