Part of Speech: Noun

Definition: a small piece of linen, silk, or other fabric, usually square, and used especially for wiping one’s nose, eyes, face, etc., or for decorative purposes.  

Source: Dictionary.com

Found in “Folding My Clothes” by Julia Alvarez

“ my panties strictly packed into the size
of handkerchiefs on which no trace
of tears showed.
” line7/line8/line9

The speaker is using handkerchief as a reference to size, by referring to something small.