Shipboard attire for most Antarctica cruises is very casual. Comfort is a priority, so wearing casual clothing, layered for warmth, is ideal. Sportswear is generally acceptable, perhaps even in the evenings for dinner. Plan to wear rubber-soled, flat or low heeled shoes for activities on deck, and it's suggested that you bring a windbreaker for places with more moderate temperatures. Most companies stress packing light so "dressing up" is of little importance in Antarctica.
For lines that do enforce a dress code, most evenings are informal -- coats and ties are not usually required, except when special events are planned. In this case, you'll want to wear something dressier for the captain's welcome or farewell dinner. Longer cruises that spend time in Antarctica may have formal nights for dinner in other destinations.
Casual: Slacks and sports shirt for men (no jeans); slacks and blouse, dress or pantsuit for women.
Informal: Most evenings call for a jacket with or without a tie for men; dress or pantsuit for women.
Formal: Dark suit or tuxedo for men; evening gown or cocktail dress for women. In general, the longer and more expensive (per day) cruises will be the most formal on formal night, but a dark suit and tie is acceptable attire on even the most exclusive ships.
Your Vacations To Go cruise specialist can advise you on the dress code for your specific itinerary.