The “Zeppelin NT” blimp balloon I used is no longer available, sadly. You can try a 40" letter I or number 1 balloon, but these are shorter and tend to give about 10 to 20% less lift.
99%+ Helium (have your balloon inflated at your local balloon shop, after preparing it as shown in step 2).
An ultra micro receiver with two servos and ESC (Electronic Speed Control) operating on a single cell rechargeable Lithium battery (1s Lipo). The Spektrum AR6400L brings al this, integrated on a tiny print at a mere 3,9 g.
A matching transmitter, I used a Spektrum DX6I, but a even the simplest, like the DX5E or the type that comes with RTF RC planes would work too. As long as it is compatible with the receiver.
A DC brushed motor under 4 grams (3 grams is better) and matching propeller. I used a motor from a micro servo and tested some propellers I had lying arround, but you can get both from Plantraco. They have great tiny motors and propellers. I would recommend the 57x20 prop for 1mm Shaft with the 7mm 3.3 Ohm motor with with nanoconnector.
A single cell lipo rechargeable battery 125 mAh, 4 g.
2.6 m of 0.14 mm2 wire and connectors matching battery and receiver.
Some scrap balsa, 1 and 4mm thick, and Tyvek (or other micro plane construction and hinge materials).
Some 3mm extruded polystyrene sheet (like Depron or Climaplan).
Two times a couple of cm of steel wire 0.8 mm diameter (or even thinner).
About 10 cm of light plastic tube, e.g. use with air filled latex balloons.
Superglue (regular or thin), cellotape, double sided tape.
Tools: soldering iron with adjustable temperature or simple soldering iron and a clothing iron, scissors, hobby knife, working surface.