The term "well-padded" implies an object or person has a generous amount of cushioning or protection. However, some antonyms for this term could include thin, bare, bony, or emaciated. These words describe a lack of padding or cushioning, and imply a lack of comfort or protection. Other antonyms could include scrawny, gaunt, undernourished, frail, or puny. These words all suggest a lack of substance or mass, which could ultimately lead to vulnerability or weakness. Therefore, while being "well-padded" may connote a sense of security, its antonyms suggest a state of fragility or inadequacy.