Black Diamond Twilight Bivy Review

Since this bivy sack was designed for light and fast missions, we decided to test it on a big wall climb in Zion National Park. With a long, gnarly approach followed by hauling gear and water up to a bivy ledge, weight was critical during our preparation and packing. At 10.7 ounces, the lightweight and compact Black Diamond Twilight certainly saved some wear and tear on our bodies. It blocked the cold wind during the breezy night and kept us dry with no noticeable condensation inside the bivy sack. Exhausted from the first day's approach, hard climbing, and hauling, we woke up re-energized thanks to a restful bivy.

Performance Comparison

Weather Resistance

With strong resistance to wind and snow, the Twilight is designed to perform in a limited range of weather conditions. It won't keep you dry during an extended heavy rainstorm. But if you're embarking on an alpine traverse or a multi-day big wall climb in the desert with a favorable weather forecast, this bivy sack will suffice.

The Twilight's NanoShield single-wall fabric design saves weight and resists wind, light rain, and snow. It is quite breathable, which is very advantageous for a bivy sack, by minimizing condensation. Our testing confirmed this breathability as well as its resistance to light rain and snow. Most importantly, it blocked the wind, keeping us warm and cozy through the night.

Weight

Okay, let's get down to the business of this bivy. The Twilight is a welterweight in the world of bivy sacks. Weighing in at 13.5 ounces, one might consider it to just be an emergency bivy sack. However, Black Diamond didn't just design it for emergencies, it's kind of like a fair-weather sleeping bag protector for a night or two spent out. In this light, it performs very nicely.

Comfort

We often sacrifice comfort during light and fast missions, which is exactly what the Twilight does. It saves weight with less material and no hooping material to keep the fabric off of your face. The zipper is lightweight because it isn't very long, which makes it difficult to get into and out of this bivy sack. The hood comes down over your eyes, which surprisingly was kind of a perk: it blocked out light and kept our eyes warm during a chilly night on a rock wall.

The most noticeable discomfort came from the tightness of this sack. With limited space around the torso, it was hard to lie on our sides and bend our knees while sleeping. The design also tapers down at the feet, so your toes hit the top of the bivy all night. We like to stretch our feet out at night and wiggle our toes, so this was not ideal. With some simple modifications, the Twilight could be made much more comfortable, without adding too much weight.

Ventilation

The Twilight has impressive breathability, with no observable condensation build-up overnight with the zipper slightly opened. However, it has a minimalist design, saving weight with a horizontally oriented zippered opening located above the chest. What this means is that when it rains, precipitation will inevitably get in if the zipper is opened for increased ventilation.

Some of the larger hooped bivy sacks rely on a flap covering a zippered opening to increase ventilation with minimal precipitation getting in. This isn't an option with the Twilight and it relies on its breathable fabric to ventilate while closed. The problem is that this leaves the fabric, yep, lying on your face.

Packed Size

If you've got big paws, this bivy sack might be close to the size of your fist. Measuring 3 inches by 5 inches, it's a no-brainer to bring it along instead of a ground tarp to protect your inflatable air mattress. Not to mention it increases the warmth of your sleeping bag. So if you're going light and fast, and the weather forecast is questionable, look no further.

Value

For what it is, the Twilight is just plain expensive. Other bivy sacks with a similar price tag have more features, are more weather-resistant, and are more comfortable overall. Improving the design of this bivy sack might make the cost more digestible, but until then, you might consider shopping around a bit.

Conclusion

We were pretty impressed with the performance of the Black Diamond Twilight, especially given how lightweight and compact it is. The breathability of its fabric was excellent, which is pretty important, given its limitations to ventilate with zippered openings. Its weather resistance was about as good as its bigger sister, the BD Firstlight tent, both of which are primarily designed for alpine missions in colder, drier weather conditions. Lacking the comfort offered by some of its competitors, it's definitely a bit pricey, but sometimes it costs you an arm and a leg to go light and fast.