Merino wool is the fleece of the Merino sheep - a breed whose origins trace back to medieval Spain, where the Spanish crown considered its extraordinary fibre so valuable that exporting the sheep was punishable by death. When that monopoly eventually broke down in the eighteenth century, the finest animal fibre in the world was suddenly available to the world, and Britain moved swiftly to acquire it.

What makes merino exceptional among all wools - and indeed among all natural fibres - is the diameter of each individual strand. Human hair averages 60 to 100 microns in diameter. Standard wool is typically 30microns or more. Merino wool, at its finest, is under 17 microns. Our PureFleece® uses 20-micron merino lambswool: fine enough that the fibres bend rather than prick the skin, creating a fabric that is both genuinely soft and structurally resilient.

Merino sheep are raised principally in Australia and New Zealand, which together supply the majority of the world's superfine merino clip each year. The finest Australian superfine grades - below 18.5 microns - are classed as Merino Royale, and command premium prices from mills around the world. The best of those mills, historically and today, have been in Yorkshire, England.

In the outdoor industry, almost every conversation about merino wool treats it as a base layer - a thin undershirt, a pair of socks, a set of thermal leggings. And while merino is exceptional in those applications, it is in the mid-layer fleece where it genuinely surpasses everything synthetic.

Standard fleece - the kind found in Patagonia, North Face, or any outdoor retailer's mid-layer range - is usually made from polyester. It is cheap to produce, light enough, and reasonably warm in dry conditions. But polyester fleece has fundamental physical limitations that merino simply does not share. It traps heat rather than regulates it. It holds odour. It sheds plastic microfibres into the air around us. And critically, the moment it gets wet, its insulating properties collapse.

Merino wool at fleece weight - we use 360gsm PureFleece® fabric - behaves like nothing else in the outdoor mid-layer category. The natural crimp of the merino fibre creates millions of tiny air pockets across the surface of the garment, trapping warm air in cold conditions and releasing excess heat in warmer ones. It does not merely insulate - it actively thermoregulates. And unlike polyester, it retains that capability even when saturated. It can actually hold 30% of its weight in water before you begin to feel it.

This is why people who cannot afford their equipment to fail choose merino fleece over synthetic. We have field-tested PureFleece® with Scottish Mountain Rescue and the Rangers of Exmoor National Park in year round conditions. In those environments, thermoregulation is not a marketing claim. It is a survival requirement.