The Sea To Summit Spark series of sleeping bags for mountaineering and hiking, which has long been a personal favorite of mine, has received a long-awaited update for the 2024 season
Sleeping bags are essential equipment for camping in the mountains, and to get a good night's sleep in them, many factors are required, including warmth, lightness, comfort, convenience, and price. However, in many cases, making something warm and comfortable makes it heavy, while making it lighter makes it cold, cramped, and uncomfortable to sleep in. To navigate this dilemma and maintain a high level of balance between each element, not only cutting-edge technology is required, but also a sense of what to eliminate and what to keep
Having looked at many sleeping bags over the years, I believe the Sea To Summit Spark series is the one that has managed to strike that difficult balance the best, resulting in the most practical product. This is the first major update to the Spark series in several years, and I can't help but be excited
This time, I was able to try out the latest, even more advanced Spark -1C and the newly released Spark Pro -1C, so I'd like to share my review of them after trying them out on a tent-camping hike
table of contents
- Main features of Sea to Summit Spark/Spark Pro-1C
- Detailed Review
- Surprisingly lightweight and compact for a full-length, full-size mummy headset
- Top-class, high-quality down that is lightweight and insulating (and also water-repellent)
- Ultra-thin, lightweight, and durable nylon fabric for a light, supple, and exquisite feel
- Waterproof and breathable material in the hood and foot box prevents the down from getting wet inside the tent
- The width is slightly wider than the previous model, providing a standard size and improved sleeping comfort
- The zipper is improved to prevent snagging and is minimal in length to reduce weight
- The "Pro" model features the highest quality down and a zipper for improved breathability, making it suitable for a wider range of temperatures
- Summary: Lightweight and insulating, this sleeping bag has evolved to be more comfortable, safe, and easy to use, making it an excellent sleeping bag for mountain use
Main features of Sea to Summit Spark/Spark Pro-1C
Sea to Summit's Spark series features a classic mummy-style sleeping bag, but with meticulous attention to detail, it's one of the lightest and most compact sleeping bags in its class. It features a high-quality 850+ FP (950+ FP for the Pro model) down filling with a water-repellent finish. The baffle design, which combines different upper and lower body structures to minimize cold spots, and draft tubes around the zippers ensure efficient, high-quality warmth. The lightweight design, including the ultra-thin 10-denier nylon fabric and a shorter zipper, ensures the bag is officially weighing less than 500 grams (619g for the Pro model) while providing insulation that can withstand temperatures down to below freezing. The new Spark Pro model, introduced this season, features a sub-zipper for flexible temperature regulation, providing comfortable sleeping in a wide range of temperatures. Offering premium comfort and warmth with a minimalist design, the Spark will keep hikers warm through the night from spring to fall, prioritizing weight and performance
Favorite points
- Surprisingly lightweight and compact for a full-length, full-size mummy headset
- Extremely high quality 850FP (950FP for professionals) down that is water-repellent and resistant to getting wet
- Ultra-thin outer fabric for a light, supple, and exquisite feel
- Waterproof and breathable material in the hood and foot box prevents the down from getting wet inside the tent
- A clever baffle structure and draft tube that prevent cold spots
- (Professionals only) Zippers for feet and hands allow for a wide range of temperature adjustment when it gets hot
- (Professionals only) The fully openable zipper allows you to combine two sleeping bags to accommodate two people
- Versatile with few drawbacks
- Affordable price for a high-quality, high-performance sleeping bag in the same class
Points of concern
- The shorter zipper makes it difficult to regulate the temperature when it gets hot and stuffy (normal)
- While multiple zippers are convenient, they can be cumbersome to operate and have drawbacks such as weight and flexibility (Pro)
Main specifications and evaluation
| Item Name | Sea to Summit Spark -1C (Regular) | Sea to Summit Spark Pro -1C (Regular) |
|---|---|---|
| Suitable height | 185cm *Women's models also available | 185cm |
| Storage size | 13.5 × 19.5 × 34cm | 13.5 × 19.5 × 34cm |
| Fabric material |
|
|
| Insulating material | 850+ Premium Goose Ultra Dry Down (RDS Certified) | 950+ Premium Goose Ultra Dry Down (RDS Certified) |
| official weight | 493g | 619g |
| Down Weight | 265g | 310g |
| Official lower limit temperature | -1°C (ISO23537) | -1°C (ISO23537) |
| size | From top: 155 / 135 / 102cm | From top: 155 / 135 / 102cm |
| accessories |
|
|
| Outdoor Gearzine Review | ||
| Comfort | ★★★★★ | ★★★★★ |
| Thermal insulation | ★★★★☆ | ★★★★★ |
| weight | ★★★★☆ | ★★★☆☆ |
| Storage capacity | ★★★★☆ | ★★★☆☆ |
| Ease of use | ★★★★☆ | ★★★★☆ |
| durability | ★★★☆☆ | ★★★☆☆ |
| versatility | ★★★★☆ | ★★★★★ |
Detailed Review
Surprisingly lightweight and compact for a full-length, full-size mummy headset
The Spark series has a classic "mummy-style" sleeping bag design, which is typical for mountaineering sleeping bags. The padding is fully enclosed, including the back and head area. The regular size is also quite long, suitable for people up to 185cm tall, so the average Japanese person should not find it too cramped. Long sizes (up to 198cm) and women's models (no pro sizes, up to 170cm) are also available to suit taller and shorter people
So, even though they haven't paid much attention to weight reduction, they are still lighter and more compact than competing sleeping bags, which has always been a major attraction of this sleeping bag. The Spark weighs 493g, and with specifications that can withstand temperatures below freezing, it is a very competitive weight at less than 500g. *The "Pro" model is not as light as the Spark series due to the zipper, which will be explained later
When packed into the included compression stuff sack, the Spark can be compressed to about the same height as a 500ml plastic bottle (see photo below)
For reference, here's the size when packed. The Spark Pro (left) doesn't get that small, but the Spark (right) can be compressed quite a bit
How is it possible for a sleeping bag with such conventional construction and sufficient warmth for three seasons to be so light? The secret lies in the meticulous selection of materials and construction, which does not compromise on either performance or lightness in every detail. Let's take a look at this in more detail
Top-class, high-quality down that is lightweight and insulating (and also water-repellent)
The highest quality down that has been an attraction since the first generation of the Spark series was developed is still present in this edition
In terms of fill power (FP, loft), which indicates insulation (quality) per weight, down is considered high quality with a fill power of 600 or above, and the finest down with a fill power of 800 or above. The down used in Spark is sustainably sourced (RDS certified) and boasts a loft of 850+ FP (Pro even boasts a loft of 950+ FP). Furthermore, the down used is high-quality goose down with larger feathers. Looking at the market at large, it can be said to offer some of the lightest and most insulating down available
What's more, this down has been treated with a water-repellent coating beforehand, making it less likely to get wet (less likely to absorb moisture) than normal. Down loses a significant amount of its heat retention when it gets wet, so its vulnerability to getting wet is said to be down's weakness (compared to synthetic fiber filling). This water-repellent treatment protects the down from water vapor in the air, making it suitable for camping in a tent in even harsher environments
It is no exaggeration to say that Premium Goose Ultra Dry Down is the strongest down available today, as it is top-class light, warm, and also does not get wet easily
Furthermore, the structure and placement of the baffles (partitions) that are filled with this excellent padding have also been given special consideration
By using different baffle structures for the upper and lower body, we aim to achieve maximum comfort with a limited amount of down
The chest area has a box structure (creating a more three-dimensional and spacious space) to enhance heat retention, and a vertically arranged baffle structure to prevent the feathers from shifting even when the baby turns over in bed (photo above, left)
The bottom half of the sleeping bag is sewn horizontally (right in the photo above), with a sewn-through construction that emphasizes a balance of warmth, breathability, and lightness (sewn through the front and back fabrics). The body mapping design for this area ensures that the limited amount of padding is placed in a way that maximizes warmth and comfort
Ultra-thin, lightweight, and durable nylon fabric for a light, supple, and exquisite feel
The tightly woven 10 denier ultra-thin nylon fabric is light, supple and comfortable against the skin
The outer and inner lining of the main body are made of ultra-thin 10 denier nylon fabric. It is tightly woven to prevent down loss and is treated with a durable water-repellent finish, making it extremely thin and lightweight without sacrificing durability
I particularly like the silky soft and smooth feel of the liner fabric against my skin, and just this comfort alone made me want to make it my regular sleeping bag for mountain trips
Waterproof and breathable material in the hood and foot box prevents the down from getting wet inside the tent
The foot area is three-dimensionally shaped to fit the shape of your feet (not surprising for a sleeping bag of this class), reducing unnecessary stress while also preventing you from getting cold by stuffing it with ample padding. Even more fortunately, the fabric around the feet and head is made of waterproof and breathable material, which effectively improves the waterproofing of this area, which often sticks to the side wall of the tent
The feet (and head) are cut three-dimensionally to fit the shape of the tent, and waterproof and breathable fabric is used to prevent water from seeping in through the tent walls
The width is slightly wider than the previous model, providing a standard size and improved sleeping comfort
The previous Spark model was not particularly wide, but this new model is slightly wider than the previous model, allowing you to relax more comfortably inside the sleeping bag. The finest, cozy down gently wraps you up in a light, fluffy embrace (without constricting you)
The overall width has been slightly increased compared to the previous model, and there is almost no longer that feeling of crampedness that is common with lightweight models
It's true that this has slightly increased the weight, but as someone who has had the disappointing experience of buying a sleeping bag in the past that was too narrow and cramped due to being lighter, I welcome this improvement in comfort
The zipper is improved to prevent snagging and is minimal in length to reduce weight
The zipper on the left side has been upgraded to include a guard to prevent the fabric from getting caught, making it easier to use (see photo below)
Furthermore, it has a double zipper that can be opened and closed from both the top and bottom, so you can keep the neck area closed and put just your left hand out, or open your upper body to adjust ventilation (right photo below)
However, as the Spark-1C is designed to eliminate unnecessary elements as much as possible, the zipper is short, reaching only down to the waist (see photo below, left). While this has the advantage of being lightweight, it is inconvenient in hot weather, such as summer, as it makes it difficult for heat to escape, so I would never consider taking the Spark-1C to a low mountain in midsummer
On the other hand, professionals can open up the entire area, including the feet, allowing for more flexible use even in hotter temperatures (see photo below, right). In this regard, professionals are one step ahead when it comes to comfort across a wider range of temperatures
The zipper opening range is significantly different between the Spark and Pro. The Spark Pro (right) has a main zipper that can be opened from the top as shown in the photo, and if you also open the zipper at the feet, it can be fully opened and used as a blanket
Both the Spark and Pro have a padded draft tube behind the zipper to keep out cold air
The "Pro" model features the highest quality down and a zipper for improved breathability, making it suitable for a wider range of temperatures
As mentioned earlier, the main difference between Spark and Spark Pro is that the latter uses lighter and warmer premium down, 950+, and the other difference is that the sleeping bag's main zipper is longer and a sub-zipper (free-flow zipper) has been added, making it more convenient and easier to regulate body temperature across a wider range of temperatures
Specifically, there are zippers on the main left side, as well as on the right side and at the feet, and by opening them you can take your arms and legs out of the sleeping bag and sleep while keeping your extremities cool (see photo below)
It is easy to adjust so that professionals can sleep comfortably with both arms and legs exposed even when it is hot. The use of the highest quality 950+FP down is also to prevent the weight increase caused by the addition of this zipper
Furthermore, if you open all the zippers completely, it can also be used as a blanket (see photo below)
These zippers allow pros to sleep comfortably in the cold of early spring and early winter, as well as in midsummer by exposing their limbs or using it as a quilt, making it truly three-season comfortable. Considering that it's hard to imagine using the standard Spark in midsummer, this versatility is a significant advantage
However, the advantages of the Spark Pro, such as its lightness and ease of use, cannot be ignored.Whether you choose versatility for a variety of seasons, scenes, and uses, or a tighter fit for a more limited range of uses, both have high base quality, but the decision is left to the user
Summary: Lightweight and insulating, this sleeping bag has evolved to be more comfortable, safe, and easy to use, making it an excellent sleeping bag for mountain use
The Spark series was already known for its light weight and high insulation, and with this update it has become even more comfortable to sleep in (despite a slight increase in weight), and the small details have been improved to make it safer and easier to use, so you could say that the overall balance as a lightweight sleeping bag has improved. This is something I highly praise, and for me it remains one of the top three standard mummy-style sleeping bags for mountain climbing
The new Spark Pro expands its use from the previous lightweight hiking-oriented model to a wider range of seasons and activities, and I think it will appeal to people who don't need extreme lightness and want a sleeping bag that can be used all year round. In that sense, I personally plan to use the Spark-1C, a legitimate evolution of the previous model (in terms of mountaineering style), for fastpacking and river climbing in the future
This lightness (high insulation per weight) is of course ideal for speed hiking and fastpacking. And its straightforward, orthodox construction makes it perfectly suitable for general mountaineering and rigorous mountaineering. The appeal of this sleeping bag is that it can be easily adapted to a variety of uses
And finally, let me emphasize this one thing: the amazing price. It's incredibly cheap, considering that it's such a high-quality, highly refined product, and that it's an overseas brand. That said, this affordable price only lasts until August, and once the extraordinary discount campaign by the importer, Lost Arrow, ends, this low price may also end, so be careful
If you're someone who only knows Japanese-made sleeping bags, you should definitely try this one out. You'll be amazed at how high its quality is. Be sure to pick one up in store this summer and check it out
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