'81' series are color corrective filters that 'warm' bluish tones. They are available in two strengths (A & B) with 'A' being the milder warming effect.
Sunpak 81B Warming Filter Features
Reduces excess blue from flash indoors or in daylight flash-fill.
Warms (balances) sea, sky and high altitude shots.
Adds healthy look to skin tones shot in open shade or overcast.