Sudsy is the adjective from suds. It describes something full of soap bubbles, or covered in them — sudsy water, a sudsy sponge, sudsy hands. It can also describe a soap that makes a lot of bubbles: "this shampoo is very sudsy". It is a light, everyday, slightly warm-sounding word, more common in American English and more common in advertising and casual speech than in careful writing. It stays close to the sink and the bath; you would not use it about sea foam or beer foam. Note the spelling — the e of a word like "soapy" has no partner here; you just add -y to suds.