Step 1:
Take a white a4-size paper.
Prefold over these two lines.

Step 6:
Repeat step 3 and 4 (folding both parts in half two times).

Step 5:
Valley-fold over this (prefolded) line.

Step 2:
Prefold over these 3 lines, use the prefolded lines of step 1 as guidance.

Step 4:
Valley-fold over these two lines, then unfold the folds of step 3 and 4.

Step 3:
Valley-fold over these two lines.

Step 10:
Mountain-fold over these two lines.

Step 8:
Turn the model.

Step 9:
Push the edges in the direction of the arrows.

Step 7:
Make an inside reverse fold on these four places. The top of the igloo will be 2x2 prefolded squares in size, see picture as help.

Step 16:
Press the layers between the arrows against each other. Then lock them together by making a valley-fold over the short blue lines.

Step 15:
Make an inside reverse fold over these three lines.

Step 12:
Press the layers between the arrows against each other. Then lock them together by folding over the short blue lines.

Step 11:
Make an inside reverse fold on these four places. All valley-folds are already prefolded.

Step 14:
Make an inside reverse fold on these two places.

Step 13:
Fold over these two lines.

Step 19:
Turn the model

Step 20:
This is a top view of the igloo....

Step 18:
Fold these two parts upwards too.

Step 17:
Fold these two parts of the edge upwards, see blue lines.