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Thermal Layer System

A thermal insulation system using Thinsulate® to completely surround the foot with no cold spots. The Thinsulate® lining is fixed in place with minimal use of adhesives to maximize loft. The base of the boot is uniquely insulated with triple Thinsulate® to minimize heat loss through the sole unit.

TLS is a thermal insulation lining system which uses layers of Thinsulate® to completely surround the foot without cold spots. The Thinsulate® lining is fixed in place with minimal use of adhesives to maximize the loft and warmth of the lining. The floor of the boot is also insulated with a triple Thinsulate® layer to insulate the floor of the boot from conductive heat loss to the ground, especially important when crampons are fitted. This full Thinsulate® lining which extends underfoot gives Boreal mountain boots a significant warmth advantage.

XTP Footbed

The Extreme Thermal Protection footbed has superior thermal insulation performance to help protect against extreme cold. XTP is used on our Mountaineering and Expedition boots.

The XTP (extreme thermal protection) is a special footbed with superior thermal insulation. The XTP footbed is made from a combination of a highly isolative felt material and a memory foam layer for superb underfoot comfort. XTP can be found in our Expedition and Mountaineering boots where it helps to protect against extreme cold.

Ref. 47503 SIULA

Bridging the gap between our G1 Lite and G1 Expe models, Siula is perhaps the most versatile high altitude boot available. Warm enough for the coldest alpine conditions and tough enough for multi season use, Siula is the ideal choice for alps in winter and 7000m summit bids.

Product Info
  • UPPERS: Composed of three layers: A fully integrated outer gaiter, mid-layer shell and removable inner bootie

  • OUTER BOOT: Integrated gaiter constructed from 2 materials: Outer portion of gaiter in abrasion resistant and highly breathable material with waterproof membrane. Inner portion of gaiter extra reinforced with super durable and tear resistant material. Premium quality waterproof TIZIP. Shell: One piece lightweight Teramida with Lorica and neoprene. 6mm EVA foam insulation layer and Cordura waterproof breathable lining. 1.4mm neoprene insole for thermal insulation. Easy to use 'Tanka' lace closure system. Lightweight TPU rand for durability

  • INNER BOOT: Bootie made from very lightweight and extremely insulative triple layer laminate. A heat reflective aluminium film is bonded to a durable polyurethane outer layer and insulative EVA foam on the internal side. BorealDry-Line® waterproof breathable lining with fully thermosealed seams. Triple Thinsulate®layers (no adhesives used) suround the foot guaranteeing maximum thermal protection with no cold spots. The sole of the bootie is covered with a durable textured TPU surface. Easy adjust 'Tanka' and strap closure system with adjustable fit around the instep area

  • MIDSOLE: Ultralight Boreal PBG-680 carbon composite midsole with lateral torsion control. Unique Thinsulate® lining for superior underfoot thermal insulation

  • SOLE: Vibram Teton rubber outsole with dual density EVA and PU shock absorbing layers. Differential hardness TPU toe and heel pieces for automatic crampons

  • USAGE: Very cold conditions and high altitude mountaineering. Long winter alpine ascents

    WEIGHT: 2580 grs./pair (size 7 UK)


  • Like G1 Expe, Siula is a triple layer boot with an integrated outer gaiter, mid layer ‘shell’ and a removable inner bootie. The fully integrated outer gaiter keeps the elements out and is neatly and simply closed with a single premium quality water resistant zipper. The gaiter is reinforced with an extremely rip resistant material in the high wear zones and the new synthetic rand material is lighter and warmer than rubber and won’t perish in the high U.V light conditions found at high altitude. Inside you’ll find an upper made from lightweight synthetic textiles and our new ‘Tanka’ closure system which is simple, secure and easy to manage even when wearing gloves. The shell is insulated with 6mm of EVA foam and lined with a super tough waterproof/breathable Cordura reinforced laminate.

  • The all new inner bootie is made from a very lightweight and extremely warm triple layer laminate material comprising of an outer polyurethane layer, heat reflecting aluminium film and an inner layer of insulating EVA foam. Triple Thinsulate™ layers fully surround the foot providing yet more insulation with no cold spots and a fully waterproof breathable Boreal Dry-Line® lining guarantees to keep your feet dry. The ‘Tanka’ and strap closure is easy to use and is adjustable around the instep area for a custom fit. Siula is fully compatible with automatic crampons and uses dual density crampon lugs, hard at the rear for a secure fit and soft at the front for reducing vibration when front pointing on bullet hard ice.  The advanced carbon composite midsole is rigid, yet incredibly lightweight and ample underfoot cushioning is provided by dual density shock absorbing PU and EVA layers. Finally, our choice of a deeply lugged Vibram® Teton outsole will help keep you upright on the approach.