I'm a long-standing fan of Mantas, originally because they were so much lighter than my Meindl leather B2s.
But Dan says in this article:
...that they're not the lightest.
So what *is* the lightest B2 boot?
Ribelle Techs apparently come in at 610g/boot, but are also apparently at the bendier end of the scale for a B2 boot.
What's a B2 boot? I'm asking rhetorically mind... The lightest I've got/used that I've climbed in crampons in are http://lightfromthenorth.blogspot.com/2017/12/scarpa-zodiac-tech-gtx-review.html followed by https://www.ukclimbing.com/gear/footwear/mountain_boots/all_round_b1-b2_mountain_boots-11233#Dolomite
La Sportiva Trango Techs might be B2? And they're very light. Definitely slightly more flexible than my old Mantas though. I've got a pair of Scarpa Charmoz too (the old blue type) and they feel very similar stiffness wise to Mantas but again significantly lighter.
Foot size comes into play, not just because of the obvious "less weighs less" but because smaller boots tend to be proportionately stiffer (or smaller feet exert less leverage). So if you're twinkletoed you may well have a wider choice of light boots you could climb in.
IIRC Scarpa Charmoz and Triolet are lighter than Mantas. They have a noticeably thinner vibrate sole block than, say Mont Blancs.
I've got ome Scarpa Rebel Pro GTX. They're a B2/3 and about as ight as they come. Absolutely love them...
Hi, I have a pair of Scarpa Charmoz OD and a pair of Ribelle techs...both the original and the 2.0 version.
All rated B2. The Charmoz are a fair bit stiffer than either pair of Ribelles tho at a (quoted) extra 200 odd g.
The Ribelles climb rock far more nimbly and are a good bit warmer... especially the 2.0 version. Static in winter in the Charmoz my feet get cold fast.
1220g per pair for the 2.0 Ribelles. More snug fit than the originals. And a closer feel in fit to the Charmoz...both of which suits my narrow feet.
I'd you want to move fast and have warm feet the Ribelles are amazing, at a price.
I'd you're not racing up and down the Charmoz are more like a lightweight workhorse...tho not great if you forsee hanging about in the depths of winter.
Hope this helps. P
North Face Verto S4K GORE-TEX Boots....B2, wideish fit
I find them light and nimble, good for rock climbing, waterproof but not very warm.
Pair said to be 1472 grams (don't know for what size though).
The Mammut Taiss Light GTX actually wins this one by a country mile. 550g per shoe in size 42.
If its still of interest my North Face Verto S4K GORE-TEX Boots are 1560g pair in size UK10.5. Obviously by no means the lightest though.
If by B2 you mean it has a heel insert to fit a C2 crampon, the lightest is the Scarpa Ribelle S at 440g/shoe https://en.scarpa.net/product/20546138/ribelle-s-hd-ribelle-line-fast-light-alpinism-black-red
If you want a stiff B2, the Lowa Alpine SL is the lightest fully rigid boot at 550g/shoe https://www.lowaboots.com/mens/mountaineering/alpine-sl-gtx-flame It has the stiffness of a B3 boot but lacks the front welt to fit C3 crampons. No insulation and not as comfortable to walk in as a regular B2 boot.
Neither of these boots are suited for typical UK conditions and are designed for summer high alpine environment.