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	STEALTH FULL SET - TM2 BLACK set with TBF fins £39.99
Value Combo Set - Mask + Fins + Snorkel Size 5 to 10.5 £17.99	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 13 UK - BLUE £24.99
Two Bare Feet FULL set with Clear HYDROSPLITS Size 4 - 13 UK - Suits Medium to X-Large face £39.99	TBF Combo ADULT Set - Mask + Fins + Snorkel Set - RED Size 4 to size 13 UK - RED £24.99
Typhoon - Hydrosplit NEW TM1 Adult SET - Blue Size 4 to 13 - Suits Small to large face £49.99	TBF Combo ADULT Set - Mask + Fins + Snorkel Set - BLACK Size 4 to size 13 UK - BLACK £24.99
Typhoon - Hydrosplit NEW TM1 Adult SET - Titanium Size 4 to 13 - Suits Small to large face £49.99	TBF Combo ADULT Set - Mask + Fins + Snorkel Set - AQUA Size 4 to size 13 UK - AQUA £24.99
TYPHOON NEW TM2 SET with HYDROSPLITS Size 4 - 13 UK - Suits Medium to X-Large face £44.99	Typhoon TM3 PINK FULL SET - HYDROSPLIT FINS Size 4 - 13 UK £49.99
Typhoon LADIES FULL SET - YELLOW Size 4 - 13 UK £49.99	TYPHOON NEW Classic SET with HYDROSPLITS - Yellow mask Size 4 - 13 UK - Suits Medium to X-Large face £49.99
TYPHOON NEW Classic SET with HYDROSPLITS - Blue Size 4 - 13 UK - Suits Medium to X-Large face £49.99	Typhoon LADIES MASK WITH T-JET FINS - YELLOW Size 4 - 10.5 UK £44.99
Two Bare Feet PINK FULL set with HYDROSPLITS Size 4 - 13 UK £39.99	Atomic ** MEGA ** Set The best mask - The Best Snorkel + Split Fins Size 4 - 13 UK £99.00
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 Combo KIDS Set - Mask + Fins + Snorkel Set - PINK Size JUNIOR 9 to size 4 UK - PINK £19.99	TWF BASIC JUNIOR KIDS Set - Mask + Fins + Snorkel Set - BLUE Junior 9 - 13 only £9.99
TBF SILICON Combo ADULT Set - Mask + Fins + Snorkel Set - RED Size 4 to size 13 UK - RED £34.99	TBF SILICON Combo ADULT Set - Mask + Fins + Snorkel Set - AQUA Size 4 to size 13 UK - AQUA £34.99
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	LADIES PINK FULL Set with PINK fins Sizes 4 - 10.5 £44.99