Boys Rectangular Bag 40 Degrees Hyper Blue. Weâre constantly testing our products in the worst conditions all around the world to make our products perform even better. Explore how we test, and share your toughest moments of testing with us in the reviews below. The Youth Rectangular Sleeping Bag has a lightweight durable 210T polyester taffeta shell, soft anti-pilling brushed polyester fleece liner, and is filled with a 4-hole hollow fiber polyester insulation to rate this bagâs comfort levet at 40 degrees F.