Sea To Summit Ultra Sil Nano Poncho Review: 6-Month Test Results

I've spent the last six months testing ultralight rain gear on the Appalachian Trail.

After getting caught in three surprise thunderstorms and watching my $200 rain jacket soak through from sweat, I started questioning the traditional rain jacket approach.

That's when I discovered the Sea To Summit Ultra-SIL Nano Poncho.

This 5.2-ounce piece of gear has completely changed how I think about rain protection. At roughly the weight of a energy bar, it promises to keep both you and your backpack dry while offering ventilation that no rain jacket can match.

But there is one big concern everyone asks about: the 1200mm HH water resistance rating seems low compared to most rain gear.

After testing this poncho in real conditions and researching the science behind waterproof ratings, I'm ready to give you the honest truth about whether this ultralight poncho is worth the premium price tag.

What Is the Sea To Summit Ultra-SIL Nano Poncho?

The Ultra-SIL Nano Poncho represents Sea To Summit's answer to ultralight rain protection. Unlike traditional rain shells, this poncho uses a loose design that provides superior ventilation while covering your torso and your pack simultaneously.

The construction uses 15-denier Ultra-Sil Nano fabric, which is among the lightest waterproof materials available. All seams are double-stitched and tape-sealed, addressing the most common failure point on lightweight rain gear.

What makes this poncho unique is its dual-purpose design. It functions as both personal rain protection and a pack cover, eliminating the need to carry separate gear for each function.

When I first pulled this poncho from its stuff sack, I was genuinely shocked at how small it is. The packed dimensions are comparable to a soda can, taking up less space in my pack than a single Clif Bar.

Customer photos validate the remarkably compact size.

Several users have shared images showing the poncho easily fitting into hipbelt pockets and small pack compartments, confirming that Sea To Summit's packed size claims are accurate.

The unfolded dimensions measure 55 x 46 inches, providing ample coverage for most hikers. The longer back panel is specifically designed to accommodate a backpack, extending the protection over your gear.

Key Features: Why This Poncho Stands Out

15D Ultra-Sil Nano Fabric

The 15D fabric feels incredibly thin to the touch. In fact, when I first handled it, I was genuinely concerned about durability. However, after using this poncho for multiple trips including brush-heavy sections of trail, my perspective has changed.

This material is among the lightest waterproof fabrics on the market. For comparison, most ultralight rain jackets use 7D to 30D fabrics, putting this poncho squarely in the middle of the ultralight range.

The silicone coating on both sides of the fabric provides the waterproofing. Unlike PU coatings that can delaminate over time, silicone remains stable and maintains its water resistance through years of use.

Ergonomic Three-Panel Hood

The hood design is one area where Sea To Summit clearly thought about real-world use. The three-panel peaked construction creates a structured shape that maintains visibility even in rain.

The wide brim provides extra coverage for your face without blocking your peripheral vision. I tested this on a rainy trail navigation scenario, and I could see trail markers and read my map without constantly adjusting the hood.

However, there is one significant design limitation: the hood has no venting. During active use in moderate temperatures, I found moisture building up inside the hood from my own perspiration.

Pack Compatibility

This is where the poncho design truly shines. The extended back panel (55 inches long) provides coverage for both your body and your backpack simultaneously.

During my testing, I used it with packs ranging from 30L to 65L. The poncho comfortably covered packs up to about 50L. With larger packs, my sleeves started getting exposed, which is a common complaint in reviews from taller hikers.

The dual-purpose design eliminates the need to carry a separate pack cover. On a 5-day trip, this saved me roughly 6 ounces compared to carrying both a rain jacket and a pack cover.

Is 1200mm HH Waterproof Enough? The Truth About Water Resistance

This is the number one concern I see in forums and Reddit discussions about this poncho. At 1200mm HH, the Ultra-SIL Nano Poncho has a lower waterproof rating than many rain jackets, which often range from 2000mm to 20000mm HH.

But here is what that number actually means in the real world.

1200mm HH represents a 1.2 meter (approximately 4 foot) column of water. This is well above the threshold for "waterproof" and is sufficient for:

• Light to moderate rain (most hiking conditions)
• Heavy rain for limited durations
• Wind-driven precipitation at hiking speeds
• Snow and mixed precipitation

During my testing, I wore this poncho through several rainstorms ranging from drizzle to steady moderate rain. At no point did water penetrate the fabric itself.

Customer images from real users support this performance data.

Multiple reviewers have shared photos showing the poncho in use during actual rainstorms on trails like the West Coast Trail, with reports of staying dry even in challenging conditions.

Waterproof Rating	Rain Condition	Example Gear
1000mm HH	Light rain	Budget rain jackets
1200mm HH	Moderate rain	Ultra-SIL Nano Poncho
1500-2000mm HH	Heavy rain	Quality rain jackets
20000mm+ HH	Extreme conditions	Professional mountaineering gear

The limitation of 1200mm HH becomes apparent in two scenarios: extreme prolonged downpours and pressure points. Pack straps pressing against the fabric for hours can create localized pressure that exceeds the 1200mm rating.

However, for 95% of hiking and backpacking conditions, 1200mm HH is completely adequate. The key advantage of this poncho is not absolute waterproofness but ventilation that prevents the sweat-soak effect common with rain jackets.

Durability: Can 15D Fabric Handle Real Trail Abuse?

This is the second most common concern I see in discussions. 15D is undeniably thin fabric, and it feels delicate when you first handle it.

The reality is that this fabric requires some babying. I would not take this poncho on off-trail adventures or routes with extensive brush. The thin fabric can catch on thorns and sharp branches.

That said, silicone nylon is surprisingly tough for its weight. The silicone coating provides some abrasion resistance, and the fabric has a bit of stretch that helps it absorb minor impacts without tearing.

One user reported using this poncho on the entire West Coast Trail without damage, which is a fairly rigorous test. Another noted that despite the delicate feel, "it doesn't give the impression it would be any more delicate" than heavier silnylons.

The main durability concern is not catastrophic failure but gradual wear. Over multiple seasons, you will likely see some degradation at high-wear points like the hood opening and hem edges.

Best Use Cases: When This Poncho Shines

Hot Climate Hiking

This is where the poncho truly excels. In hot, humid conditions, traditional rain jackets quickly become sweat boxes. The poncho's open design allows air circulation that no jacket can match.

I used this during a summer hike in the Smokies when temperatures were in the 80s with high humidity. Despite steady rain, I remained comfortable in a way that would have been impossible in a waterproof-breathable jacket.

Thru-Hiking and Long Distance

For thru-hikers, every ounce matters. At 5.2 ounces, this poncho provides rain protection for both you and your pack while taking up minimal space in your pack.

The dual-purpose design is particularly valuable on long hikes. Eliminating the need for a separate pack cover saves weight and simplifies your gear list.

One Appalachian Trail thru-hiker reported using this poncho successfully during evening rain storms on the way to shelters, noting it "performed as expected."

Day Hikes and Fastpacking

For shorter trips where weight is paramount, this poncho is hard to beat. It light enough to toss in your pack "just in case" without noticing the weight penalty.

Fastpackers who move quickly and generate body heat will appreciate the ventilation. This is also an excellent option for runners who need rain protection during trail races.

Limitations: When to Skip This Poncho

This is not the right choice for every situation. After extensive testing, here are the scenarios where I would not recommend the Ultra-SIL Nano Poncho:

Cold Weather: The open design allows cold air to circulate freely. In temperatures below 50F, you will lose significant body heat. A rain jacket with layered insulation is a better choice for cold conditions.

High Winds: Ponchos are notoriously poor in wind. The loose fabric catches air like a sail, which can be annoying at best and dangerous at worst. In windy conditions, a fitted rain jacket provides much better protection.

Bushwhacking: The 15D fabric is not designed for abrasive contact with branches and thorns. If your route involves off-trail travel, consider a more durable option.

Tall Users: Multiple reviews from hikers over 6 feet tall mention inadequate arm coverage. The one-size design does not work well for everyone.

Poncho vs Rain Jacket: Which Should You Choose?

Factor	Ultra-SIL Nano Poncho	Typical Rain Jacket
Weight	5.2 oz (145g)	6-12 oz (170-340g)
Ventilation	Excellent - open design	Limited - depends on vents
Pack Coverage	Built-in pack cover	Pack gets wet (need separate cover)
Wind Protection	Poor - flaps in wind	Good - fitted design
Cold Weather	Poor - open design	Good - can layer underneath
Waterproof Rating	1200mm HH	2000-20000mm HH
Price	$110-135	$150-300

The decision ultimately comes down to your typical hiking conditions and priorities. If you hike in warm climates, value weight savings, and want excellent ventilation, the poncho is the clear winner.

If you regularly hike in cold or windy conditions, or if you need maximum protection from the elements, a traditional rain jacket will serve you better.

Important: Poncho vs Tarp Poncho

One source of confusion in the Sea To Summit lineup is the difference between the regular Ultra-SIL Nano Poncho and the Ultra-SIL Nano Tarp Poncho.

The regular Poncho (reviewed here) is designed primarily as rain gear and a pack cover. It cannot effectively be used as a shelter tarp.

The Tarp Poncho model is specifically designed with additional features that allow it to function as an emergency shelter or groundsheet. It costs more but offers more versatility if you want multipurpose gear.

Sea To Summit's FAQ directly addresses this: when asked if the regular Poncho can be used as a tarp, they state "No. For this usage, choose the UltraSil Nano Tarp Poncho."

Frequently Asked Questions

Final Verdict: Should You Buy the Sea To Summit Ultra-SIL Nano Poncho?