From the product description, check product page for current description, price and availability:

These Erlenmeyer flasks help the best brewers to make large yeast starters to get their beer fermenting fast. Large populations of active yeast help ensure a healthy fermentation, free of off flavors.  One of our favorite things about the Erlenmeyer flasks is that you can boil your starters directly in them!

Our large 2000ml Erlenmyer Flask is the ideal vessel to make a large yeast starter for 5 gallon lagers and high gravity brews. Because it is made from borosilicate glass you can move it from a boil on your gas stove into a cold water bath for cooling, without the risk of cracking. (We do not recommend the use of an electric element. If this cannot be avoided, we recommend using a larger pot as a hot water bath on the stove.) This means you can do the whole process in one container, keeping it simple and helping to reduce the risk of contamination when transferring from one container to another.

Recommended Process for Use of Flask:
Double Boiler Method

It is important for your safety to heat water in the flask with a heat source that distributes heat evenly. Our manufacturer has confirmed that direct heat to the glass can break down its integrity and break if the heat source doesn’t distribute evenly.

Morebeer! recommends using the “double boiler method.”  This process involves using a boiling water bath on the outside of the flask to heat up the water inside the flask.  All you need is a kettle 3 gallons or larger.  This process is much safer and efficient. If the flask should break or boil over, your kettle will be there to collect the contents, thus keeping your stove clean and keeping you away from potential harm.

Features

• Massive 2L (2000mL) Capacity
• Made from Borosilicate Glass
• Fantastic price for a flask of this size
• Produced for MoreBeer!
• 6.5″ base 2.5″ top 10.75″H

Why make a yeast starter? (from our FAQ)
We build starters for 3 main reasons. First, to ensure yeast health. By making a starter 1-3 days in advance, you ensure that your yeast is healthy and strong and ready to do its job. Second, to create more yeast. By making the starter you will increase the cell count of the yeast, giving you a better chance of keeping bacteria’s and wild yeasts from fermenting your wort. Third, if you are making high gravity beers. If you are making a high gravity beer (1.060+) you will need more yeast to start the ferment faster. High gravity beers will also finish more completely when you pitch ample quantities of yeast.

In the lab world, these flasks are known as “Student Grade”. A great flask for making yeast starters!(Student grade is not the highest grade flasks and will have minor defects)