Here's another example of a built-in foldable. 

Under each flap, you can have students write the definition, or draw the phase change representations. Then, next to the word, on the next page, you can have them do something else. Below is an example of how students can then make more meaning by drawing or writing to describe an everyday example.

This is a great foldable to help organize thoughts on structure and function.
First you fold the top and bottom corners in to make a sideways house. Then, label the side of the page with the adaptation (leaves). You may want to flip the structure and function locations. 

Then, underneath you can either provide the structure, and the students have to come up with the function, or vice-a-verse. 

The beauty of these foldables is that there is no pasting or stapling of papers into the journals. You simply use the pages that are already in the journal. The following example really requires only 1 page from the notebook, but I used the page behind to pose a question "What happens in..."

The purple lines indicate a cut. The blue paper is inserted to help differentiate between different pages. 

When you flip each tab, there's a written explanation and a diagram. 

Here's a foldable for density that uses 2 consecutive pages. Density is written in graffiti style letters on the back page. The front page is folded over in half and there's a cut down the middle. You can easily have students write down examples of things that float or sink under the appropriate flaps. 

When you completely flip over the first page, under the graffiti letters is a definition of density and diagrams that represent different densities. Note that the least dense is still on the left and the most dense is on the right.