A day or so after adding yeast to my first ever three batches of Mrbeer wort a thin layer of foam appeared and covered the surface. It was about 1/8" thick. At the time I found it fascinating and impressive.
I went to my local homebrewery and picked up a half batch of some fresh stuff.
I recently made a simple batch of wort from cracked grain and LME and used refrigerated Muntons yeast.
WOW!! The Krausen was at least 1 inch thick!!
I have it sitting in water in a cooler on my lanai. When I open the cooler to check the temp the CO2 and the fermenting smell is almost overwhelming.
P.S. Mrbeer kits RULE because they are small enough to fit in coolers.