The lower total volume and weight means it does not cost as much to ship for the equivalent final volume. Starting in 2015, UPS and FedEx began calculating shipping charges by the greater of the actual weight and dimensional weight for packages.

Example:

You want to order 10 Liters of BG-11 Medium:

• For the 1-Liter Algal Culture Media, you would need to order a quantity of 10 bottles. When shipping costs are calculated, the total combined weight of 10 bottles, and the size of the box needed for that number, would need to account for approximately 25 lbs. (~11.34 Kg). 
• If a Media Kit can prepare 10 Liters of media, but omits most of the water, then shipping costs are calculated with the weight of the concentrated solutions, or approximately 2.5 lbs. (~1134 g). Add the savings to the generous discount the Kits provide on a per Liter basis and you are left with a cost-effective solution to your media needs.