Particle board is just what it sounds like; for interior only, it's a high mass concoction of sawdust and glue. Very nice for heft and sound-control.
Mineral core if for fire doors. You usually don't need that, just in specific code-enforced places where a 2 hour fire rating is called for.
Hollow core is just like it sounds, two sheets of surface (plywood or masonite, etc) with air in between. Actually there are little strips of cardboard hot glued in here & there so it doesn't collapse inward. Poor/fair sound control characteristics, feels light and hollow 'cause it is.
Last month I hung two pairs of paint-grade french doors; they were masonite veneer over a lumber core of finger-jointed knotty pine. More knots than pine.
Lumber-core w/veneer of clear wood is now typical for stain-grade solid doors.
Casey

Jeld Wen makes many composite doors in many configurations so they can't be separated just by core construction. Start with the facing, then select the core and frame (perimeter structure).

Jeld Wen paneled doors are divided up into 3 categories with different core & frame options in each category.

CUSTOM CARVED
These doors are faced with sheets of MDF with a routed panel pattern (cut with a router) on a finger-jointed or stainable pine frame.
The core options are:
(1) honeycomb paper
(2) celotex

MOLDED
These doors are faced with wood/plastic composite sheets that have been pressed with heat to approximate the appearance of recessed panels.
The core and frame options are:
(1) PROCORE - Solid core particle board core with a combination wood/MDF or all wood frame
(2) Solid mineral core with an all wood frame (firerated)
(3) Hollow core (with strip spacers) with MDF frame

FLUSH
These doors are faced with 1/8" hardwood veneer or pre-primed/unprimed/pre-finished hardboard.
The core and frame options are:
(1) Solid particle board core with wood or MDF frame
(2) Solid mineral core with mineral composite frame
(3) Solid wood stave core with wood frame
(4) Hollow core/corrugated honeycomb cell filler with a combination wood/MDF frame.

MDF is not a problem for a bathroom.

I recommend buying doors from a door and window supplier and avoiding Home Depot and Lowes. You can never be sure Jeld Wen doesn't make a lower quality product for retail outlets and the professional suppliers will give you better information, possibly a lower price, and deliver the right doors on time especially if a builder or design professional is involved.

I’d be careful when buying JW doors altogether. I paid extra for solid core doors only to get them and realize they weren’t. It was obvious too. They sounded hollow when I knocked on them. I called a representative from the company and they told me it was a dense foam center. Well I didn’t order and pay for a dense foam door. I wanted and paid 50% more for a solid door. They told me too bad so sad.

Thanks for sharing your experience, James. Yikes!