There are many varieties, shapes, sizes, colors of the konjac sponge. The seller that I buy mine from on amazon for $6.99 claims they are "natural fiber + natural green tea ingredient." There are also French clay, charcoal, bamboo, turmeric, volcanic scoria... Each touting their own benefit.
Traditionally, these sponges are made from Konjac fibers with is a potato plant that grows readily in Asia. It's soft texture gently exfoliates and the fibers have a natural alkaline pH so the sponge will balance out the acidity of the facial impurities.
Our skin is protected from the acid mantle which is comprised of sebum and sweat, killing harmful bacteria. Healthy skin has a pH of 5.5 which is slightly acidic. Oily skin, like mine, is too acidic. The goal of my skincare regiment is to balance out my skin without wiping out my acid mantle. I used to over cleanse my skin and slather oil free products on it which would just cause more oil production.
The alkaline (basic) nature of the Konjac sponge helps to balance out my skin externally. Internally this can be done by eating berries, apples and tomatoes. If you have dry skin, which is alkaline, this sponge may tip you to far into a high pH. However, a little exfoliation is good for everyone. It feels really nice on the skin and leaves my face extremely soft and makeup application is a breeze afterwards.
The Konjac sponge should be replaced within 3 months. You will be able to tell when it's time to pitch it. I'm on my second and they are extremely durable. Just be sure to keep it moist. If you are using it twice a day, that shouldn't be a problem but be sure to rinse your facial cleanser out thoroughly. I stick with a foaming (or non-foaming) or gel based cleanser as an emollient, cream based cleansers are difficult to rinse out.
Have you tried a Konjac sponge? What are your thoughts?