The front is made with Polartec Alpha Direct (136g/m²) for warmth and breathability, while the back uses highly breathable Shadow Rip for better airflow where a pack tends to trap heat.

It pairs especially well with our highly breathable UL All-weather series , so give that combination a try.

With Polartec Alpha Direct insulation placed only on the front, this vest keeps your core warm while allowing excess heat and moisture to escape. The result is exceptional breathability that helps maintain a comfortable body temperature during high-output activities.

Layer a shell or shirt over the Alpha Vest for added warmth. This is especially helpful when you stop to rest.

When a down jacket feels like overkill, the Alpha Vest is a great alternative for staying warm at night—without the bulk.

The front of the vest features Polartec Alpha Direct, offering an ideal balance of warmth and breathability. In contrast, the back and shoulders use ultra-thin, highly breathable Shadow Rip—with no insulation at all.

Why the difference? When you’re on the move with a pack, your back and shoulders heat up fast. And when you’re sleeping, that same area is pressed against a pad, compressing any insulation and rendering it ineffective. So instead of adding bulk where it won’t help, we focused warmth where it matters most: the front.

It’s no match for 1000 fill-power down, but the 136g/㎡ Polartec Alpha Direct used in the Alpha Vest is one of the warmest active insulation fabrics out there. While it shines during movement, it’s also warm enough to double as a reliable insulation layer during rest stops.

The below chart compares the 1000 fill power down and other insulators used in thermal clothes on the market.

• Heat retention is measured by JIS L1096A, in Yamatomichi in-house test. The heat insulation property is measured from the amount of energy consumed by the heat-generating element to maintain its temperature. The maximum value is 100%.
• The values of Polartec and Primaloft fabrics are the manufacturers’ catalog specs. Other fabrics’ values are measured by Yamatomichi. 1000 fill power down includes its 7 denier nylon outer and lining.

Polartec Alpha Direct is used on the front for excellent breathability. It keeps you warm without trapping too much heat or moisture, so you stay comfortable while moving.

The below chart compares the breathability of middle layer products*.

*Measured by JIS 1096A (Frazier method), in Yamatomichi in-house test.

The chart below compares the drying performance of different midlayer products. While Alpha Direct does not dry as quickly as the exceptionally fast-drying Shadow Rip used in the UL Shirt, its moisture content after spin-drying is much lower than that of wool and many other fabrics. Even when wet, it dries quickly when lightly wrung out or simply worn for a while.

*Tested by Yamatomichi. This comparison shows the moisture content remaining after the fabrics were fully soaked and then spin-dried for 15 minutes. Higher values indicate more retained moisture and slower drying.

Like other synthetic insulations, Polartec Alpha Direct absorbs very little moisture and maintains its loft even when wet. That means it continues to provide warmth when you sweat or get caught in light rain.

It is lighter than a standard T-shirt and packs down to about the size of a soda can.

The mountains can be harsh, with unstable weather, sharp temperature swings, strong winds, and intense sunlight. In these conditions, both breathability and wind resistance are essential. Our newly adopted Teijin Shadow Rip fabric delivers that balance while remaining lightweight and durable.

Thin, lightweight fabrics often use a ripstop structure, with thicker yarns woven into a grid to improve tear resistance. However, this can also create a rougher surface that is more prone to pilling through friction.

Shadow Rip is made with fine, high-strength yarns that create a smooth surface with excellent resistance to friction. The result is a fabric that is lightweight, durable, soft to the touch, and resistant to wrinkling.

While the Alpha Vest is lightweight and warm, its structure—where lofted fibers are attached to a mesh fabric—can lead to some fiber shedding over time with wear or washing.

• Use a neutral detergent. Machine wash on a gentle or delicate cycle at 30°C or below.
• Wash separately or use a laundry net.
• If the back fabric becomes wet with sweat and remains in contact with white or light-colored wool or silk garments for an extended period, color transfer may occur.
• Wash after use to remove sweat.
• Avoid bleach and fabric softener.
• Do not iron or dry clean.
• If necessary, wash before first use to remove any loose fuzz from the fabric.