Updated Firstlight
Black Diamond gave the Firstlight tent some new materials. It now features their proprietary NanoShield single wall fabric, and the floor is comprised of 70D polyester. The two tents are shown side by side below; the model we tested is shown first, and the updated Firstlight is shown second.
We're linking to the new model now, but the review to follow is still our account of the previous version.
Performance Comparison
Despite some new competition in the market, the Firstlight is one of the best bivy tents out there. While it doesn't do everything incredibly well, it's a fantastic option for trips where the weather is likely to be good, and weight and packed size are your top priorities. It's one of the absolute lightest models and compresses down to the smallest size of any 4-season tent we tested. The downside: it isn't waterproof — in the rain, you are almost certain to get dripped on — and the walls will become thoroughly saturated, soaking anything that touches them.
It can handle moderate wind okay but isn't nearly as strong as most of the models in this review. As it's so small, this is certainly not our first pick for spending lots of time inside. However, it's a reliable option for fast and light trips where weight and packed size matter the most.

While the Black Diamond Firstlight isn't necessarily the best all-around four-season tent, it is an excellent option for certain trips where weight and compressed size are of the utmost importance. The Firstlight is seen here in its element, camped in Washington's North Cascades.
Photo: Ian Nicholson
Ease of Set-Up
This 4 season tent pitches from the inside, with the ends of the poles inserted into reinforced corners, and Velcro strips that wrap around the poles along the walls. These strips are located at various points in the tent and help keep them in place. If it's windy and you don't use them, the tent will be significantly weakened. The interior pitch does take a little longer to become accustomed to and become efficient at pitching.
If it isn't super windy out, we like to set it up while standing up - versus getting inside of the tent.

The Firstlight sets up from the inside. Its poles are held in place by Velcro tabs and by reinforced corners containing a metal grommet for the pole. This is a pretty bomber system, but when placing the pole into the grommet, you do need to take care not to stab a hole through the thin floor.
Photo: OutdoorGearLab Team

This shelter uses an internal pole setup without pole sleeves. Instead, the poles are supported by the walls of the tent and held in place by Velcro loops like the one pictured here.
Photo: Ian Nicholson
Weather Resistance
Weather resistance is the biggest trade-off.
This contender uses fabric that is highly water resistant, though not waterproof. The Firstlight is okay when used in shorter thunderstorms or light rainstorms, but in heavy rain, wet snow, or extended rainstorms, the fabric will become thoroughly saturated, and you'll get some (or a fair amount of) dripping on the inside, no matter how well you seam sealed it. To make matters worse in these wetter conditions, the walls will become completely saturated, and anything that touches them will get wet, which is a bummer if two people squeezed inside.

The Firstlight is only water-resistant, and the seams aren't taped. It will do okay in drier snow, and it will protect you from the wind, but if it's raining or the snow is wet for any length of time, it will drip on the inside. You can seal the seams yourself (as shown here), which helps a little, but not much.
Photo: OutdoorGearLab Team
It performs best in dry conditions or when it is well below freezing (if it's precipitating), as the drier snow won't saturate the fabric as quickly. However, wet snow will have the same or even worse effect than extended rain showers.

This is an excellent shelter for most short fairweather trips. It keeps you out of the wind and sun and still works great in a light rain or snow storm.
Photo: Ian Nicholson
For milder weather conditions, the fabric is more breathable than others. You can also leave the door partially or fully open. It does okay in moderate wind, as it has a basic design and minimal guy points.

The perfect application for the Firstlight -- a multi-day ski tour in AK. This tent is best for trips where weight and compressed volume are paramount, and it's unlikely to rain.
Photo: OutdoorGearLab Team
Livability
Bivy tents are relatively cramped and uncomfortable. We don't recommend them for anything but alpine climbing, multi-day ski touring, or any other trip where the user is willing to sacrifice comfort for weight savings and maximum packability.
This tent used to be considered micro, with only 27 square feet of interior floor space. Now it's small, but not tiny. While 27 square feet isn't big, you can still fit two regular-sized pads side-by-side with no problem. However, people taller than six feet will have their heads and feet touch the ends of the tents.
Durability
No ultralight tent, especially one this light, is that durable. If you're after low weight and minimum bulk, rather than extreme toughness, this is the tent for you.

The Firstlight has a guy point at each corner.
Photo: Max Neale
The Firstlight has a relatively fragile sil-nylon floor that doesn't hold up to rocks or sharp pine cones well; take care when pitching it in particularly rocky places. The fabric is not waterproof, but it does keep the water resistance over a decent amount of time, provided that care is taken to dry it out and keep it clean.

The Firstlight is the same size as the I-tent (27.3 square feet). Here, though, we compare it with the slightly bigger Eldorado, which at 30.8 square feet is 5" longer and 3" wider.
Photo: Ian Nicholson
Weight/Packed Size
Without guylines, this model weighs a mere two pounds 13 ounces — or three pounds five ounces with everything you need to make it functional (guylines, pole bag, etc.). When it came out, it was game-changing.

There are many good four-season contenders, and they each excel at different things. Some are stronger, some lighter, some more adaptable. Therefore, it is essential to figure out your needs and what types of trips you plan to use your tent for. Here, we're testing on the East Ridge of Eldorado, North Cascades, WA.
Photo: Ian Nicholson
Minimal weight and crazy small packed size are why you buy this tent. In some cases, it's even half the size of other single wall tents! Seriously, the body packs up smaller than a Nalgene bottle, and the poles break down to some of the shortest in the review.

While it may have a few drawbacks regarding livability and performance in wetter storms, for long approaches or carry-over style climbs, the weight and the packed volume of the Firstlight is tough to beat. Here, the Firstlight is camped out below Mt. Shuksan's Price Glacier, which requires carrying all your gear up and over the mountain and down the other side.
Photo: Ian Nicholson
Versatility
This tent isn't super adaptable or versatile, mainly because it's not waterproof or super strong, and is tiny. However, it performs well in desert climates because its relatively cool and can provide a nice place to hang out while being protected from the sun.
It does have bug netting, allowing you to ventilate when the bugs are horrible, which was a HUGE advantage for climbing in the lower-48 and Southern Canada. In an alpine environment, this tent rarely has the problem of finding a site (or ledge) big enough to set the tent upon. Its small footprint can be pitched almost anywhere that two people can lay down.

The Firstlight has a vent on the back of the tent. This helps to keep moisture build-up down, but when it's raining outside the walls will become wet regardless.
Photo: Max Neale
Features
While this tent doesn't have a lot of extra features, it prioritizes low weight and minimum bulk. It does offer a small vent on the back and a little awning on the front to help with ventilation. It features a bug screen mesh door on its only entrance and two small pockets. Did we mention how small this tent packs up?

Blue skies and tight camping spots? This is the Firstlight's domain.
Photo: Ian Nicholson
Value
While this tent isn't as versatile as others, it's very good at what it does. It's far less expensive than many single-wall tents out there, and is a great value.

The Firstlight is one of the least expensive products in our review. It is a great fair weather bivy tent for shorter trips, but it isn't as versatile as many other contenders in our review, which all offer unique advantages.
Photo: Ian Nicholson
Conclusion
The Black Diamond Firstlight is dang sweet for what it's designed for — fast and light trips where weight and packed size matter more than anything. If you want a tent that will hold up in storms, is more versatile or is just comfortable to hang out in, regardless of the length of the trip, we'd strongly recommend considering a different model. However, for shorter, fair-weather trips with a good outlook, this model disappears in your pack like no other and is considered a game-changer for its weight.

Small footprints aren't just important in the greater ranges. Here Dan Whitmore appreciates the small footprint of the Firstlight, waking up with nearly 2,000 feet of air below after a stormy night on a very small bivy ledge. Buttress of Mt. Goode, North Cascades, WA.
Photo: Ian Nicholson