A soft, down-turned, asymmetric shoe from Boreal's high-end Trilogy range, which also includes the Dharma and Satori, the Synergy excels at bouldering - whether that be on steep limestone, smeary gritstone or indoor climbing.

Forefoot

The business end of the Synergy is, as you would expect for a soft shoe, pretty soft - although not as soft as some of the extremely soft models we've seen on the market recently. I've found this to be a good thing as it means you can still transfer power through your foot rather than simply relying on toeing-down on holds. It also means that the Synergy has some longevity in the forefoot rather than wearing out as soon it sees a rough foothold, as the super soft shoes often do. In fact, after having used my pair of Synergys for a couple of months I have seen very little wear on the toe.

Retaining some stiffness in the forefoot also enables the Synergy to be a brilliant shoe for bouldering both on steep, edgy problems and on vertical, smeary problems. As it's a soft shoe it's great at smearing, giving maximum contact with the rock, but as there is still a bit of stiffness in the forefoot you can squeeze out some power on steep edges. The toe itself is extremely accurate and sensitive which is a blessing for all types of holds. I feel very confident in my foot placements wearing the Synergy which makes it an easy and reliable choice for hard bouldering.

Midsole

The Synergy's softness comes from its lack of a midsole. This softness is great for bouldering as it gives maximum sensitivity and, as it allows your foot to bend severely, it enables you to transfer maximum tension and power to your forefoot. The combination of sensitivity, flexion and power makes it great for smearing and for volumes (aka competition climbing). As we see indoor climbing holds, and particularly competition holds, move towards a larger and more rounded profile, the advantage of shoes such as the Synergy grows. Conversely, I find that a soft shoe can also be good for the smaller holds found outdoors, including atypical and small edges, as it allows your toe to 'splurge' over the foothold giving maximum contact. The disadvantages of a soft shoe, and particularly one with a soft (or non-existent!) midsole, are that it is unsupportive and therefore uncomfortable and not as good at edging over time as a stiffer, more supportive shoe. However as the Synergy is intended for bouldering this is not an issue.

Although the Synergy does not have a midsole it does feature 'Boreal's Wrap Rand tension system'. This is a rubber strip which runs around the back of the heel and under the middle of the foot. This provides additional support (welcome in a shoe with no midsole) and creates extra tension from the heel to the midsole. This extra tension transfers lots of power to the toe and the heel.

Uppers

The Synergy features plush, modern uppers similar to the Dharma and Satori. This includes a large rubber toe patch with a raised toe knuckle (although not as severely raised as the Dharma). The rand and toe patch are made from a single piece of rubber giving a precise, molded feel to the top of the shoe and there is also an area of Friction Skin rubber coating for extra sensitivity when toe hooking. All in all this makes the Synergy excellent for toe hooking due to the rubber coverage, sensitivity and how close to the foot the upper feels.

The lined synthetic upper and elasticated tongue give a great sock-like fit and they are very comfortable to wear. The Synergys are tightened up by two straps: one main strap which does most of the business and one smaller strap for minor adjustments (although these seem to be so minor on me that they are unnoticeable).

Fit

Unfortunately there is no low volume/women's version of the Synergy. The fit is fairly high-volume in the forefoot due to the raised toe knuckle and a relatively wide profile. This width extends back towards the heel with a fairly wide upper above the midsole which can be tightened by the straps. The molded heel cup is snug although there is a little space around the sides of my heel and it does add some unnatural depth and width to your heel which is not necessarily an issue, although it is a little unusual. There is lots of tension in the heel nevertheless.

I wear an EU 45 in street shoes and wear the Synergy in 44. One EU size down from your street shoe provides a snug and comfortable fit. If you want to go for high performance at the expense of comfort I would recommend going down a further half size from your street shoe size.

Rubber

The shoe features 4.5mm of Boreal's own Zenith Ultra rubber (which is the same compound that the Satori uses, whereas the Dharmas use the stiffer Zenith Pro). For shoe nerds, the Zenith Ultra rubber is similar to Vibram Grip in that it's fairly soft and focussed on being sticky rather than edging. It compliments the construction of the Synergy nicely, providing softness in the toe of a slightly stiff forefoot. I've found the Zenith Ultra rubber to be good - it's not going to blow you away but equally there isn't much noticeable difference in performance to the ubiquitous Vibram rubber.

Summary

The Synergy is an excellent choice for bouldering outdoors and indoors. It manages to retain the advantages of a soft shoe - sensitivity, maximum contact and flexion - whilst maintaining enough stiffness and precision to perform well on edges, as you would expect from a stiffer shoe. In addition it's comfortable, albeit fairly high volume and, whilst specifically a bouldering shoe, it's a great choice for any rock (or plastic) type.

Boreal say:

Synergy is designed for optimum feel. A highly aggressive last shape is carefully blended with superb sensitivity and supremely sticky BOREAL Zenith Ultra™ rubber to enhance the natural qualities of the foot; a true synergy of design, materials and craftsmanship, enabling you to push your limits on any bloc, both indoor or on rock.

The most sensitive shoe in our collection. Single strap for heel security with excellent flexibility. Minimalistic construction allows maximum precision and sensitivity. Combined with a unique one-piece heel cup and wrap rand, this shoe is optimised to perform at the highest level.

• Sizes: 4-12 UK (men's fit only)
• Upper: Microfibre upper. Combined elastic and strap closure. Elasticated tongue integrated in the upper. Minimalistic rubber toecap as protection and for outstanding grip
• Lining: Yes

For more info see borealoutdoor.com

• Midsole: No
• Construction: Slip-lasted
• Sole: Ultra sticky BOREAL® Zenith Ultra outsole. 4-4.5 mm thickness depending on size
• Usage: Bouldering, competitions and steeply overhanging rock