I bought the Nimbus 13 to replace my worn out pair of Nimbus 11.  Asics Nimbus shoes are the most comfortable I have ever worn.  The Nimbus 13 are very comfortable out of the box and require no break in time at all.  They have a memory foam cushion around the heel area that molds to your foot.  The insole is also made of memory foam and provides very good cushioning.