Two jackets, three different weather situations - triclimate jackets are based on the original mountain layering system and, as such, are really versatile. For the ThermoBall™ Eco Triclimate Jacket, we've combined a waterproof, windproof and breathable 2.5-layer DryVent™ shell with a recycled polyester insulation layer. What's so special about that? The ThermoBall™ Eco insulation maintains its warmth even when wet, making it the perfect partner to a waterproof shell. Wear them together on days when the weather really tests your resolve. On cold but dry days, you can wear the ThermoBall™ insulation on its own. When it's wet, blustery and mild, opt for just the DryVent™ shell. The shell is made using stretchy fabric and it has underarm vents, so you can keep it on and stay comfortable even when you're charging up hill in a downpour.