Confused? Here's what to look for:
Masks are made from 3 types of material:
PVC - a cheaper product and harder. Therefore not so comfortable on the face.
Silitex - A slightly better form of PVC
Silicon - VERY comfortable on the face and can be worn for a longer period. Also, has a much better seal against the water getting in. The silicon masks are generally made to a higher quality
My preference is for a silicon mask. I would not dive or snorkel with anything else.
Masks are designed to cover the nose to stop you sucking in water when using a snorkel. The nose area can be pinched so that you can equalize when diving down or using scuba equipment.

TBF SILICON + Q Combo ADULT Set - Mask + Fins + Snorkel Set - BLUE Size 4 to size 13 UK - BLUE £34.99	TBF SILICON FULL SET - BLACK set with TBF fins £34.99
COZUMEL ADULT Set - Mask + Fins + Snorkel Set - BLUE Size 11 to size 13 UK - BLUE SPECIAL PRICE WHILST STOCKS LAST £19.99	TBF Combo ADULT Set - Mask + Fins + Snorkel Set - PINK Size 4 to size 13 UK - PINK £24.99
Two Bare Feet FULL set with Blue HYDROSPLITS Size 4 - 13 UK - Suits Medium to X-Large face - DRY TOP OPTION £39.99	TBF Combo ADULT Set - Mask + Fins + Snorkel Set - BLUE Size 4 to size 12 UK - BLUE £24.99
TBF Combo ADULT Set - Mask + Fins + Snorkel Set - YELLOW Size 4 to size 12 UK - YELLOW £24.99	Typhoon - Hydrosplit NEW TM1 Adult SET - Blue Size 4 to 13 - Suits Small to Medium face £49.99
TBF Combo ADULT Set - Mask + Fins + Snorkel Set - BLACK Size 4 to size 12 UK - BLACK £24.99	TYPHOON NEW TM2 SET with HYDROSPLITS Size 4 - 13 UK - Suits Medium to X-Large face £39.99
Typhoon LADIES PINK TM3 FULL Set with PINK T-JET fins Sizes 4 - 10.5 £44.99	Typhoon LADIES MASK WITH T-JET FINS - YELLOW Size 4 - 10.5 UK £44.99
SEAC SUB STEALTH X-PRO FULL SET £76.99	TBF Combo KIDS Set - Mask + Fins + Snorkel Set - BLUE Size JUNIOR 9 to size 4 UK - BLUE £19.99
TBF Mask Snorkel and T-JETS FULL Snorkelling SET - BLUE Size 4 - 10.5 ADULT including DRY TOP Option SILICON £35.99	TBF SILICON Combo ADULT Set - Mask + Fins + Snorkel Set - BLACK Size 4 to size 13 UK - BLACK £34.99
TBF SILICON Combo ADULT Set - Mask + Fins + Snorkel Set - PINK Size 4 to size 13 UK - PINK £34.99	Anti-Fog liquid *****MUST HAVE***** £4.99
SEAC SUB Snorkelling snorkeling Vest £22.99	SEAC SUB STEALTH KALIBRA FULL SET £59.99
ALL BLACK set 5 TBF SILICON + ADULT Set - Mask + Fins + Snorkel Set Size 4 to size 13 UK - black £34.99	BEAVER ANTI-GLARE Diving Mask + Snorkel + Fins Choice of Snorkel and Fins £48.99
LADIES PINK TM2 FULL Set with PINK T-jet fins Sizes 4 - 10.5 £44.99	Sphera + Flexar fins FULL Snorkel SET ULTRA Lightweight full travel set - ML size only 1.3kg £52.99
TBF Combo KIDS Set - Mask + Fins + Snorkel Set - BLACK Size JUNIOR 9 to size 4 UK - BLUE £19.99	Beaver Mask Strap cover - Choice of colour £4.99
BODYGLOVE - KIDS FULL BLUE SILICON Snorkelling SET mask snorkel + fins Size junior 10 to adult 4 UK With Smaller mask and snorkel set £28.99	BODYGLOVE - KIDS FULL PINK SILICON Snorkelling SET Mask Snorkel + fins Size junior 10 to adult 4 UK With Smaller mask and snorkel set £28.99