1.9 Double D’s (Double Black Diamond) enhancement inserts are a hybrid 3d printed insert that uses the stock foam that comes with you tires to create a 2 stage insert!!  This design allows for trimming and tuning of the stock foam to create the tire softness or firmness you desire.  The cupped shape locks the foam onto the insert so it can’t shift like other two stage foam inserts. 
This inserts are designed to fit the rim ring rather than the tire so no need to pay for tire specific inserts, these can be used with any size 1.9 tire.  There are glue channels in the print if you rim ring  size is a little bigger as some brands are. With the use of “Shoe Goo” type glue to help keep them from shifting. (Glueing the insert to the ring)
Currently there is 4 sizes available to fit most 1.9 wheel/tire combos.  Sold as a set of 4
1.9 Smalls are for 0.8” or 19mm rings
(For Class 1 or smaller tires or very narrow tires)
1.9 Medium are for 0.8” or 19mm rings
1.9 large are for 1.0” or 24mm rings
 1.9 CF are for the Amazon style Carbon Fiber wheels.