The Ingress Protection Rating, abbr. IP Rating is a measurement of how well a product is sealed against water or dust. It is an international standard developed by the IEC (International Electrotechnical Commission) to help end consumers measure the protectiveness of waterproof backpacks (and more!) before they make purchasing decisions.
The IP rating come in 9 different levels for the protection against water, marked from IPX-0 to IPX-8.
IPX-0: Not protected from water
IPX-1: Resistant to water dripping vertically.
IPX-2: Resistant to water sprays at an angle up to 15 degrees.
IPX-3: Resistant to water sprays at an angle up to 60 degrees.
IPX-4: Resistant to water splashes from all directions.
IPX-5: Resistant to low-pressure water streams.
IPX-6: Resistant to high-pressure water streams.
IPX-7: Resistant to water immersion at a depth of up to 1 meter for 30 minutes.
IPX-8: Resistant to water submersion deeper than 1 meter.
IPX-7 and IPX-8 ratings can be listed together with IPX-0 to IPX-6. For example, a dry bag can be IPX-6/IPX-8 if it can stand against high-pressure water streams and submersion deeper than 1 meter.