Today’s technique is the pop-up box.
To make it easier for you I made a template as well > 1box-popup-card
Trim your cardstock to 29.5cm x 12cm. The pop-up box card will fold flat to fit a 6″ square envelope.
Score at 1.5cm, 8.5cm, 15.5cm and 22.5cm and across the longest length 5cm down from the top. With the 1.5cm tab on the left side cut along the score lines down to the middle line and trim the tab leaving only the bottom side.
Do not fold the upper flaps yet.
Cut three 2cm x 10cm strips of white cardstock, score at 1.5cm from each end and fold. Affix the strips to the inside of the box, making sure they’re aligned with each other and close the sides of the box.
Fold down the flaps, except one as it will be the background of the pop-up card.