I use bolsters to fill the angle between mattress and headboard. Closure is YKK invisible zipper. Because the bolster cover squeezes inserts into the desired shape, I suggest filling them with king bed-pillow inserts.
Choosing an infill
Q: Good morning, Tricia! I just placed another order (my 4th!) ... the bolsters ... am confused as to what to put inside. Should I just buy king filler pillows and roll them up?

A: I buy synthetic fill king pillows because they are more resilient. Horrible in a pillow but just what is needed in a bolster!