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.
Red-leaved and red-speckled romaine lettuces are especially beautiful in salads. Because romaine lettuce is both crunchy and nutritious, itâs also a great choice for sandwiches. Related: The Most Delicious Lettuce Varieties Worth Planting. Butterhead, or Boston, lettuce has soft, tender, rich green outer leaves and white to yellowish hearts.