Actually, proper packing for Langtang Valley Trek (as high as 3,870m at Kyanjin Gompa) is essential. The weather can turn quickly, so layers are the best idea. Begin with dry, moisture-wicking base layers. They draw sweat away from your skin and dry quickly. Include a warm mid-layer of fleece or wool for cold mornings and nights. A down jacket for cold nights, particularly above 3,000m will be must packing list.