Conductors and Insulators. In a conductor, electric current can flow freely, in an insulator it cannot. Metals such as copper typify conductors, while most non-metallic solids are said to be good insulators, having extremely high resistance to the flow of charge through them.onductors and Insulators. In a conductor, electric current can flow freely, in an insulator it cannot. Metals such as copper typify conductors, while most non-metallic solids are said to be good insulators, having extremely high resistance to the flow of charge through them.
Butterhead lettuce. A type of head lettuce whose botanical name is Lactuca sativa var. heirloom. Two common types are Boston and bibb lettuce. Have small, round, loosely formed heads with soft, buttery-textured leaves ranging from pale green on the outer leaves to pale yellow-green on the inner leaves.
Macronutrients. The four most common types of green lettuce -- green leaf, romaine, butterhead and iceberg -- have 13 to 17 calories in 100 grams, which is about a 1/2-cup serving of shredded lettuce.They deliver 1 gram of protein, or about 2 percent of the recommended daily intake.ceberg only has half the amount of iron. The same serving size of green leaf, romaine or butterhead lettuce provides 3 to 5 percent of the recommended daily intake of calcium, magnesium, phosphorus and potassium.