MIDWEIGHT BASE LAYER - Our base layers are designed for warmth, performance (including but not limited to breathability and moisture management), and wearable comfort. The adventure is yours, we'll keep you warm and comfortable. RELAXED FIT - Designed with a looser fit that lies gently on the skin without binding. Generally, there is little to no stretch in the fabric. Therefore the silhouette is designed to accommodate movement. Often used in lifestyle wear, as well as for a base layer. WARMTH FACTOR 7/10 - Ranked from Mild to Hot, the Warmth Factor Thermometer tells you how warm each of our products is. Warmth Factors 6, 7, and 8 are considered Midweight and are very popular for most cold-weather activities. MOISTURE TRANSFER FIBERS - An essential feature in all our products, Hot Chillys exclusive moisture transfer fibers (MTF) move moisture away from your body by employing hydrophobic yarns to wick away perspiration, thereby keeping you dry and comfortable. These children's thermal pants are made with two layers of fabric connected back to back with open spaces between the layers to trap and hold warm air. These kids' long underwear pants are knitted with MTF soft spun polyester fibers that transport moisture away from the skin to keep you warm, dry and comfortable. Pepper Bi-Ply is a tried-and-true favorite choice for soft, comfy children's thermal pants while protecting against the cold. Features of these kids' long underwear pants: Plush-back waistband. Gusset eases movement and reduces seam bulk. MTF Moisture Transfer Fibers to keep skin dry. Spun polyester is slightly brushed for extra softness. Double layer traps air between layers for extra warmth. Flat seam construction for seam strength and longevity. Versatile for sports or everyday warmth needs. Midweight warmth, relaxed fit children's thermal underwear pants.