At the top of all the following design steps, there is a video showing the exact steps I took which are then explained as text below each video. Make sure to watch the video in HD as it helps with the clarity of the numbers I type in.All that is left is to design a more stylish and ergonomic design around this now proven concept, and to do this, I am going to use AutoDesk's free 3D CAD modelling software ' AutoDesk 123D Design ' and for these purposes I am going to design this for 3D printing on a 'MakerBot Replicator 2' (using PLA which is a non toxic biodegradable plastic derived from corn starch) or any other 3D printer/3D printing technique by taking advantage of many of 3D printing's unique attributes ( I'm not new to the world of 3D printing! ).First download and open 'AutoDesk 123D Design' available at this download link if you don't already have it and click on 'Start a New Project' (if this dialogue appears, if it doesn't, click on the 123D logo and click on the 'New' button). Make sure in the bottom right of the window it shows 'Units:mm' as this instructable uses millimeters as the units in all the dimensions, if this is not the case, hover over whatever unit is being displayed, and then select 'mm' from the drop down box.During this step, I am going to use a very powerful tool in the 123D software called 'Revolve' which allows very complex organic shapes to be created from a simple 2D sketch, this can create a lot more ergonomic and organic shapes that the simple 'Extrude' features.To start with, by using the 'Spline' and 'Polyline' tools under the 'Sketch' category at the top by clicking on the respective tool in the 'Sketch' category and then clicking on the grid to start a sketch, I drew out an ergonomic profile of the outer face of a basic cup shape. After using a tool, tap the enter key or click on the small green tick that appears to confirm the drawn line and exit the sketch. After selecting a new tool, I always made sure to select (click on) one of the previously drawn lines to make sure I was adding to the existing sketch which helps later when performing functions on this sketch (such as the 'Revolve' function I use later). After exiting the sketch, the lines and splines can still be modified by clicking and dragging respective points in the sketch, this is useful throughout this tutorial.I then added some dimensions by clicking on one of the lines I have drawn followed by hovering over the gear symbol that appears and then clicking on the 'Edit Dimension' button, I then added dimensions to appropriately size the profile by clicking on two points or lines to add a dimension between then clicking to confirm and then double clicking on the created dimension to edit it, I made the height of the cup 11mm shorter than the proposed final height of the cup (for space to add an indentation for the 10mmx1mm thick rotating 'vent covering collar' later allowing the user to select the insulating characteristics of the cup), some dimensions can also be added while drawing with certain tools such as the 'Polyline' tool by simply typing in the desired dimension while drawing a line, view the video above to see the other dimensions I used at this point.Using the 'Offset' tool under the 'Sketch' category at the top, I clicked on the profile and created three copies inside the original at distances 1mm, 6mm and 7mm away which are for the other three faces of the two walls making each wall 1mm thick (which I think is suitable for fused filament 3D printing) and creating a 5mm thick air gap between them, it is in this gap that air will either circulate to cool down the drink or insulate the cup to keep the drink warm depending on the user's preference.I then added the space for the vent covering collar at the top by adding a further 11mm height to the cup as a 10mm high indented section (by 1.1mm to hold the 1mm thick collar (producing a 0.1mm clearance when the collar is installed allowing it to be rotated easily)) to hold the collar later by using the 'Polyline' tool to draw this section as shown in the video above. As I am designing this for 3D printing, I also added a 20 degree angled line under the overhang produced by the indentation for the collar getting rid of the need to have support material printed below it in the insulation cavity as this would affect the cups functions.Using the 'Polyine' tool again I closed off each pair of lines at both ends so they would become solid shapes that can be converted to 3D.When the walls are ready to be converted to 3D, they will have a reddish hue to them, if this doesn't occur that means that the lines making up each wall are not all joined so are not continuous which I found to be the fault of the 'Offset' function as when the lines were offset, they were also split apart, to fix this, simply delete the horizontal lines that were offset during the 'Offset' operation, and then simply re-draw them back in the same place making sure each end attaches to the other corresponding lines, the walls should now have a reddish hue to them if they didn't before.Then using the 'Rectangle' tool, I added ribs of 2mmx5mm in the air gap at the bottom of the cup to support the base of the inner wall of the cup so it can be 3D printed while still trapping air to insulate and prevent heat loss through the bottom of the cup.Now I revolved the drawing using the 'Revolve' tool under the 'Construct' category at the top, I selected the two walls of the cup and the ribs at the bottom of the cup, I then selected the 'Axis' button and then selected the vertical line of the far left rib to act as the axis of rotation. Then I typed in '360' so the profile would revolve a full 360 degrees and then tapped the enter button to confirm.