Irish Moss, ESB and The Brew Shop have available Irish Moss in it’s natural form (not whirlfloc) in 50g resealable pouches
A teaspoon of Irish Moss a few minutes from the end of your boil will aid the clarity of your finished beer. Irish Moss is a charged adjunct that actually helps tannins and proteins in the hot wort coagulate and quickly fall to the bottom of the boiler while chilling your the beer. If you drop a small amount of Irish Moss in your brew you can actually see the proteins and tannins coagulate into little lumps at the end of the boil.
Whirlfloc versus Irish Moss while natural is often best it really comes down to price at $4.95 for 50g this is about half the price you will see on most brewshop websites.
Some Brewers rehydrate their Irish Moss before adding to their boil it is simple cover one teaspoon of dried product with cold water in a cup and let stand for 15 minutes. the jury’s out on this most brewers simply toss it straight into the boiling wort.