To be able to know the Propylene Glycol (PG) and Vegetable Glycerine (VG) rate of your e-liquid, you should look at the label of your e-liquid bottle this mention is written on the label.
The mention PG/VG is also indicated on websites during a purchase, you can click on the e-liquid you choose and check the rate in the description of the e-liquid.
General:
It vaporizes at relatively low temperatures. In the gaseous state, it condenses into fine droplets (generally in the presence of an airflow) thus trapping some of the neighbouring molecules (ie: nicotine, aromatic molecules, water, etc.). This rapid phenomenon produces an aerosol that visually mimics smoke.
PG (propylene glycol) is a component of the diluent matrix used in the majority of e-liquids on the market. Tested and approved by the pharmaceutical industry as a vehicle for bronchodilator active ingredients (eg Ventolin), it appears to be the ideal base for e-liquids.
The main alternative compound to PG as a carrier for the diluent matrix of an e-liquid is vegetable glycerin (VG).
When vaping, VG (Vegetable Glycerin) is transformed into a dense and abundant vapour. To taste, it is slightly sweet which masks the perception of the aromatic molecules contained in the e-liquid.
Moreover, VG is about 30 times more viscous than PG. Thus, it will have more difficulty than the PG to impregnate the wick of the personal vaporizer. There is therefore a higher risk of local drying out. To overcome this phenomenon, you have to wait for the e-liquid to re-soak the device correctly and wait a few seconds between two inhalations.
The vaper can also choose to adopt his equipment by using resistors and cotton adapted to viscous products.