Our verdict

The Allbirds Tree Flyer 2 proves that being eco-friendly isn't just for the birds. From its eucalyptus-based upper to the BioPebax midsole derived from castor beans and the heavy use of recycled materials, we can't help but love all the environmentally responsible features crammed into this shoe. What's more, we were pleasantly surprised with just how nicely it rides during our less intense daily runs. While its hefty weight and even heftier price tag are a little prohibitive, we think it is worth it to support a brand dedicated to reducing the carbon footprint of their shoes and look forward to further improvements coming in the future!

Pros

  • Environmentally friendly
  • Breathable knit upper
  • Good impact dampening
  • Snug sock-like fit
  • Accommodating toebox
  • Secure heel hold
  • Quite flexible and comfy
  • Smooth and stable ride
  • Works as a walker or gym shoe

Cons

  • Quite heavy
  • Pricey for a daily trainer
  • Not so responsive

Audience verdict

80
Good!

Who should buy

We recommend the Allbirds Tree Flyer 2 as an excellent choice for:

  • Environmentally conscious runners who want a planet-friendly option that has a much smaller carbon footprint to produce
  • Neutral runners looking for a well-cushioned and comfy daily trainer
  • Runners in warmer climates looking for a shoe with 
  • Active folks in the market for a versatile and durable shoe that can take on light trails and other fitness activities 
  • Style-minded individuals looking for a sleek and  geometric design that's good for strutting about town

Allbirds Tree Flyer 2 buy

Who should NOT buy

With its $160 price tag, the Tree Flyer 2 might be prohibitively expensive for most runners, especially for a daily trainer. We recommend checking out the Brooks Trace 2 as a more budget-friendly alternative that also makes use of recycled materials in its construction. 

The Tree Flyer 2 is a daily trainer that's best suited to less intense runs over short to moderate distances. For runners who want a shoe that is better suited to mile-gobbling long-distance sessions, we suggest the similarly stacked Brooks Launch 10 or the much more cushioned On Cloudmonster instead. 

When it comes to speedier runs, we recommend checking out the Hoka Mach 5 as a snappier alternative. 

Allbirds Tree Flyer 2 cut

Tipping our scale at 10.3 oz (293g), the Tree Flyer 2 is heavier than the average road shoe. For those who prefer a more lightweight daily trainer, we recommend the feathery Saucony Kinvara 14

Breathability

To test the breathability of the Tree Flyer 2, we sealed the shoe and pumped it full of smoke. As we can see, the smoke is able to filter through the shoe's upper with relative ease, leading us to give it a score of 4 out of 5 in this assessment. As such, the Tree Flyer 2 is a good companion for runs on warm days as it won't trap heat in like a foot sauna. 

This well-ventilated nature is easy to understand when looking at a backlit cross-section of the Tree Flyer 2 and seeing how easily the light shines through the many large pores that dot the shoe's upper. 

The knit upper itself is made from eucalyptus tree fibers that seem to be quite densely woven but still allow air to flow through the shoe and vent out any heat generated as we run. 

Allbirds Tree Flyer 2 Breathability microscope 1
Allbirds Tree Flyer 2 Breathability microscope 2
Test results
Tree Flyer 2 4
Average 3.8
Compared to 235 running shoes
Number of shoes
1
Breathability
5

Durability

Toebox durability

Interestingly for a road shoe, the Tree Flyer 2 has a bio-based TPU overlay that acts as a toe bumper with the aim of protecting the fragile knit upper. To put this protective layer to the test, we fired up our Dremel to 5K RPM and set it against the toebox with 3.2N of force. 

Powering down our tool after the four-second test, we were pleased to find that the overlay actually held up to the relentless grinding and was only left with a small indent at the point of contact. This leads us to give the Tree Flyer 2 a perfect 5 out of 5 for toebox durability. 

Allbirds Tree Flyer 2 Toebox durability damage
Test results
Tree Flyer 2 5
Average 2.4
Compared to 169 running shoes
Number of shoes
1
Toebox durability
5

Heel padding durability

The heel collar didn't fare nearly as well against the Dremel which made quick work of mincing through the lining material. 

In the wake of the test, we were left with a decently sized rip in the lining out of which our tool managed to siphon out some of the soft padding within. This lackluster performance leads us to give the Tree Flyer 2 a heel padding durability score of 2 out of 5, meaning that the shoe is susceptible to the friction of heel rubs and shouldn't be used without socks very often. 

Allbirds Tree Flyer 2 Heel padding durability damage
Test results
Tree Flyer 2 2
Average 3.2
Compared to 165 running shoes
Number of shoes
1
Heel padding durability
5

Outsole hardness

The Tree Flyer 2's outsole is about as hard as average, giving us a durometer reading of 82.9 HC. Throughout the course of testing shoes here in the lab, we found that this level of hardness usually denotes a good balance of grip and durability with only a few exceptions here and there. Let's see if the Tree Flyer 2 is one of them. 

Allbirds Tree Flyer 2 Outsole hardness
Test results
Tree Flyer 2 82.9 HC
Average 80.5 HC
We use an average of four tests. The photo shows one of those tests.
Compared to 286 running shoes
Number of shoes
52.1 HC
Outsole hardness
93.0 HC

Outsole durability

Now spinning at a more formidable 10K RPM, we set our Dremel against the Tree Flyer 2's outsole for a total of twenty-two seconds of abrasive force. 

Once all was said and done, we used a tire tread gauge to measure the indentation left behind by our tool and found that only 0.7 mm of material was lost.  This is a slightly better performance in this test than the average road shoe and means that we fully expect this shoe to hit the expected shelf life of 400 to 500 miles with some life left in the outsole yet. 

Allbirds Tree Flyer 2 Outsole durability damage
Test results
Tree Flyer 2 0.7 mm
Average 0.9 mm
Compared to 147 running shoes
Number of shoes
0.0 mm
Outsole wear
2.0 mm

Outsole thickness

Further contributing to the longevity of the outsole is just how much rubber we have underfoot to burn through before losing traction entirely. At 5 mm thick according to our caliper measurements, the Tree flyer 2's outsole it quite a bit thicker than our current lab average. 

Allbirds Tree Flyer 2 Outsole thickness
Test results
Tree Flyer 2 5.0 mm
Average 3.2 mm
Compared to 305 running shoes
Number of shoes
0.0 mm
Outsole thickness
6.6 mm

Weight

While its name implies a lightweight frame for fluttering through our daily runs, the Tree Flyer 2 is actually heavier than the average road shoe at 10.3 oz (293g). That said, it didn't feel overly bulky during our test runs or while walking around in this shoe. 

Allbirds Tree Flyer 2 Weight
Test results
Tree Flyer 2 10.34 oz (293g)
Average 9.38 oz (266g)
Compared to 306 running shoes
Number of shoes
5.26 oz (149g)
Weight
12.56 oz (356g)

Cushioning

Heel stack

At 32.1 mm thick according to our caliper measurements, the Tree Flyer 2's heel stack is just shy of our current lab average. This is still a good amount of foam underfoot to ensure well-cushioned and protective landings during our less intense daily runs. However, long-distance runners will be better served by a shoe with a higher stack like the On Cloudmonster instead. 

Allbirds Tree Flyer 2 Heel stack

The Tree Flyer 2's heel also extends outwards, which is beneficial for runners with a heel-striking stride and also makes the shoe feel very comfortable whenever we take it out for a walk. 

Test results
Tree Flyer 2 32.1 mm
Average 33.7 mm
Compared to 305 running shoes
Number of shoes
7.6 mm
Heel stack
45.7 mm

Forefoot stack

Up at the forefoot, the Tree Flyer 2's stack is right on par with our current lab average at 24 mm thick according to our caliper. This means that forefoot strikers should also enjoy landings protected from impact in this shoe while still getting some sense of the ground below for intuitive toe-offs. 

Allbirds Tree Flyer 2 Forefoot stack
Test results
Tree Flyer 2 24.0 mm
Average 25.0 mm
Compared to 305 running shoes
Number of shoes
7.6 mm
Forefoot stack
36.9 mm

Drop

The difference in our stack measurements leaves the Tree Flyer 2 with a drop height of 8.1 mm, making the brand-stated drop of 8.5 mm laudably accurate. This offset isn't too steep and should suit the needs of most runners regardless of footstrike. 

Allbirds Tree Flyer 2 Drop
Test results
Tree Flyer 2 8.1 mm
Average 8.7 mm
Compared to 305 running shoes
Number of shoes
-0.8 mm
Drop
16.1 mm

Insole thickness

At 3.8 mm thick, the Tree Flyer 2's insole is just shy of our current lab average. That said, it still provides a decently padded footbed for us to sink into as we land in the shoe. 

Allbirds Tree Flyer 2 Insole thickness
Test results
Tree Flyer 2 3.8 mm
Average 4.5 mm
Compared to 301 running shoes
Number of shoes
1.5 mm
Insole thickness
7.3 mm

Midsole softness

Note: a low durometer measurement equals a soft material, whereas a high measurement means it's firm.

We pressed our durometer against the SwiftFoam midsole and got a reading of 22 HA. This isn't exactly plush but it feels quite forgiving underfoot; baffling the impact of our landings with a soft touch that nicely mutes out the harsh road below. 

Allbirds Tree Flyer 2 Midsole softness durometer

While the midsole is a Bio-Pebax foam made from castor beans, it doesn't retain the same qualities as its non-bio formulation; namely, the responsiveness we've come to expect from Pebax foams like Nike's ZoomX as found in the Invincible Run FlyKnit 3.

Test results
Tree Flyer 2 22.0 HA
Average 21.4 HA
We use an average of four tests. The photo shows one of those tests.
Compared to 233 running shoes
Number of shoes
8.5 HA
Midsole softness (soft to firm)
41.5 HA

Midsole softness in cold

Note: a low durometer measurement equals a soft material, whereas a high measurement means it's firm.
Allbirds Tree Flyer 2 Difference in midsole softness in cold

Difference in midsole softness in cold

To observe the effects of cold conditions on the midsole, we placed the Tree Flyer 2 in the freezer for twenty minutes and then pressed our durometer against it once more. Becoming only 11.4% firmer in the cold makes the Tree Flyer 2 much more consistent than the average road shoe and means that the cushioning should feel just as soft no matter how low the mercury drops. 

Test results
Tree Flyer 2 11.4%
Average 25.5%
Compared to 232 running shoes
Number of shoes
0%
Difference in midsole softness in cold
100%

Stability

Lateral stability test

The Tree Flyer 2 feels grounded as we shift our weight from side to side in the shoe. However, as a neutral shoe with no guidance features, it does little to mitigate excessive lateral movements, making it less than ideal for those with pronounced overpronation. That said, we didn't experience any major instability during testing. 

Torsional rigidity

The Tree Flyer 2 put up a relatively high level of resistance as we bent and twisted it in our hands, leading us to give it a torsional rigidity score of 4 out of 5. This feels quite comfortable underfoot as it allows for some natural twisting of our foot while still providing a sturdy and level landing surface for surefooted landings. 

Test results
Tree Flyer 2 4
Average 3.3
Compared to 284 running shoes
Number of shoes
1
Torsional rigidity
5

Heel counter stiffness

Despite the external heel counter being made of a seemingly solid TPU overlay, we found it to be relatively pliable in our manual assessment, leading us to give it a middle-of-the-road stiffness score of 3 out of 5. This also feels quite comfortable as it holds our foot in place nicely without putting too much pressure on our heels and tendons. 

Test results
Tree Flyer 2 3
Average 2.8
Compared to 268 running shoes
Number of shoes
1
Heel counter stiffness
5

Midsole width in the forefoot

We measured the Tree Flyer 2's midsole to be 116 mm wide at the forefoot, making it quite a bit broader than our current lab average.

Allbirds Tree Flyer 2 Midsole width in the forefoot
Test results
Tree Flyer 2 116.0 mm
Average 113.8 mm
Compared to 306 running shoes
Number of shoes
100.5 mm
Midsole width in the forefoot
126.5 mm

Midsole width in the heel

The midsole isn't quite as robust at the heel which measures 88.8 mm wide. While this is narrower than our current lab average, it should still be enough of a platform for heel strikers to enjoy stable landings in this shoe. 

Allbirds Tree Flyer 2 Midsole width in the heel
Test results
Tree Flyer 2 88.8 mm
Average 90.5 mm
Compared to 306 running shoes
Number of shoes
74.9 mm
Midsole width in the heel
106.6 mm

Flexibility

Stiffness

We secured the Tree FLyer 2 to our workbench and used a force gauge to find that only 24.1N of force is needed to bend the shoe to 90 degrees. 

This is more flexible than the average road shoe and means that the Tree Flyer 2 is able to bend along with our foot with relative ease. This contributes to the shoe's easy and forgiving ride which makes it easy to wear the shoe comfortably for extended periods.

Allbirds Tree Flyer 2 Stiffness feel
Test results
Tree Flyer 2 24.1N
Average 29.1N
We use an average of four tests. The video shows one of those tests.
Compared to 288 running shoes
Number of shoes
2.2N
Stiffness
94.4N

Difference in stiffness in cold

We also repeated the flex test after letting the shoe chill in the freezer for twenty minutes and found that it only became 8.2% stiffer when exposed to the cold. This is much more consistent than the average shoe under similar conditions which, in combination with the midsole's post-freezer test, makes the shoe a decent winter training partner. We say, "decent", as the shoe's relatively high breathability means that we'll likely suffer from cold feet in extremely frigid weather. However, a warm pair of socks could help stave off frostbitten toes. 

Test results
Tree Flyer 2 8.2%
Average 35.9%
Compared to 288 running shoes
Number of shoes
0%
Difference in stiffness in cold
148%

Size and fit

Toebox width at the widest part

We measured the toebox with our caliper to be 100.5 m wide at its widest point. This is wider than our current lab average and means that the Tree Flyer 2 should accommodate runners with wide feet quite comfortably. 

Allbirds Tree Flyer 2 Toebox width at the widest part
Test results
Tree Flyer 2 100.5 mm
Average 98.4 mm
Compared to 306 running shoes
Number of shoes
89.5 mm
Toebox width at the widest part
109.1 mm

Toebox width at the big toe

Moving up to the area around the big toe, we measured the Tree Flyer 2's toebox to be 77.6 mm wide. This is right on par with our current lab average and means that we had ample room to splay out without butting up against the upper. That said, broad-footed runners of certain foot shapes who need a little more wiggle room to avoid hotspots should consider the slightly roomier Allbirds Tree Dasher 2 instead. 

Allbirds Tree Flyer 2 Toebox width at the big toe
Test results
Tree Flyer 2 77.6 mm
Average 78.2 mm
Compared to 180 running shoes
Number of shoes
60.4 mm
Toebox width at the big toe
92.5 mm

Tongue: gusset type

The Tree Flyer 2's one-piece upper construction has a sock-like fit that feels like the shoe warps itself around our foot rather than us simply sitting within. It's stretchy enough to accommodate our foot comfortably while, at the same time, elastic enough to lock us in nicely. 

Allbirds Tree Flyer 2 Tongue: gusset type
Test results
Tree Flyer 2 Sock like

Comfort

Tongue padding

With no tongue to measure per se, we pinched our caliper on the material across the instep of the upper and found it to only be 3.4 mm thick. 

Allbirds Tree Flyer 2 Tongue padding

While this isn't paper-thin, we would have greatly appreciated another millimeter or two from this daily trainer so that the laces didn't feel quite as apparent across our instep during testing. That said, using as little material as possible serves to keep some weight off this already chunky shoe and jives with the shoe's environmental ethos. 

Test results
Tree Flyer 2 3.4 mm
Average 5.6 mm
Compared to 303 running shoes
Number of shoes
0.5 mm
Tongue padding
14.2 mm

Heel tab

The inclusion of a sleek finger loop at the heel of the Tree Flyer 2 is a nice little detail that helps us slide the shoe on and off a little more easily. 

Allbirds Tree Flyer 2 Heel tab
Test results
Tree Flyer 2 Finger loop

Removable insole

The Tree Flyer 2's insole isn't glued in, so removing it in favor of a custom orthotic or an aftermarket alternative is possible if needed. 

Allbirds Tree Flyer 2 Removable insole
Test results
Tree Flyer 2 Yes

Misc

Reflective elements

Proudly emblazoned at the heel of the Tree Flyer 2 is a small plaque that proudly states the shoe's carbon footprint of only 7.21 kg CO2e and acts as a small reflective element for some minimal nighttime visibility. That said, we still recommend using additional high-vis gear if running along dimly lit roads at night. 

Test results
Tree Flyer 2 Yes