I needed a bag that was fully waterproof to assist me with cross training on my bike for long distance running events later on this year. The bag had to be 100% waterproof with the capacity to hold additional items of clothing, fuel and needed to be comfortable.
I came across the Sea Line Urban Waterproof Backpack and I have been very impressed with it. The bag is constructed with two pieces of waterproof seamless material that have been Thermal wielded together to create a fully waterproof bag. The bag is sealed by a water tight roll down top with an elastic quick clip closure this allows you to adjust the size of the bag to allow you to carry larger and smaller loads. There is a zip pocket on the front of the bag that allows for easy access to smaller items such as gels or maybe a map.
The Sea Line Urban Waterproof Backpack is very light, extremely comfortable with plenty room inside for storing whatever you need for a long cycle or if using as a commuter bag all you need for your work commute. The bag comes with a stowable waist belt that I found very useful if carrying heavier loads. The bag comes with a handle at the top of the bag that is very sturdy and useful for carrying the bag.
The bag comes in two sizes small 17 litres and large 37 litres and 4 colours Grey, Green, Red and Orange. One thing I found while using the backpack is the lack of an internal pockets or dividers in the bag, it is just one big pocket, while this did not bother me too much it may not suit everyone but you can purchase a separate backpack organizer that solves this. If you want a backpack that is completely waterproof and you can trust with even the most expensive electrical items while out on your bike this is a perfect match for you.
For additional information please go to the Sea Line website
Backpack
http://www.cascadedesigns.com/ie/sealline/urban/urban-backpack/product
Organizer
http://www.cascadedesigns.com/ie/sealline/urban/urban-backpack-organizer/product