The anatomy of a composite door: explained

4 min read Doors

Following on from one of our latest blog on the anatomy of a casement window, for those of you thinking about improving your security this winter, we thought it would be helpful to list the whole anatomy of a composite door.

Composite door terminology explained


The term 'composite' means made up of several parts or elements.

ABS skin

Acrylonitrile Butadiene Styrene, also known as ABS, is a robust thermo-plastic skin used to reinforce timber core composite doors. Used to prevent fading, discolouring and scratches, to understand how tough it is, it is the same material used to make Lego.

Our 48mm timber core composite doors from industry-leaders Solidor incorporate an ultra-strong ABS skin.

LVL engineered timber

Laminated veneer lumber, also known as LVL, offers an alternative to solid timber. Made by bonding multiple layers of veneer together, LVL engineered timber provides unmatched strength and dimensional stability.

Our single rebate 44mm composite doors from the Derwent range incorporate a high-grade LVL engineered timber inner frame.

GRP skin

Glass reinforced plastic, also known as GRP, is a high-impact resistant skin used to strengthen foam filled composite doors. Used to prevent fading, peeling, and warping, lightweight GRP is often used to protect and strengthen the hulls of boats. GRP can also be moulded to replicate authentic woodgrain finishes.

Accommodating a wide range of budgets, these composite door brands feature high density polyurethane foam cores protected by a durable GRP skin:

composite french door

CFC-free foam core

Composite doors with foam cores are made from high-density, CFC-free polyurethane foam. CFC-free means it doesn't contain chloroflurocarbons, which are harmful to the environment. Offering outstanding thermal performance, one drawback is that most foam filled composite doors can’t be fully recycled.

Timber core

Timber core composite doors are thicker than other types of composite doors, making them one of the strongest and secure residential door replacement options available. Sourced from sustainable forests, timber core composites can be fully recycled at the end of their useful life.

Single rebate composite door

A door rebate is the deep groove cut into the door frame that allows the slab to fit tightly against its frame. Single rebated composite doors have one groove and one weather seal.

Double rebate composite door

Double rebated composite doors feature two grooves and two weather seals. Almost twice as thick as single rebate doors, double rebate composites offer extra insulation, security, and unique triple glazed options.


Glazed side panels are positioned on one side or both sides of the door.


A glazed panel positioned above the door.

black composite door


The opening the door fits into.


A structural horizontal beam over the top of a door, generally used for load-bearing and decorative purposes. Typically found in homes built with brick or masonry blocks, lintels are usually made from concrete, timber, or steel.

Head jamb

The head, or head jamb, is the uppermost horizontal section of the door frame.


The vertical side sections of a door. The hinge side stile is the 'hinge stile' and the other side is known as the 'lock stile'.


A vertical beam that divides the frame and/or smaller glass units. Door mullions can also be used to separate two doors from each other.

Top rail

The horizontal section that sits below the head jamb.

Freeze rail

Also known as a cross rail, the freeze rail sits horizontally across the next divide down underneath the first panels on the door. (not all doors will have one)

Mid rail

The horizontal section that usually sits in line with the door handle.

Bottom rail

The horizontal section that sits above the sill/cill.

Sill / cill

Also known as the threshold, the sill/cill closes the gap between the bottom of the door and the floor.

Weather bar

Also known as a weatherboard, the weather bar is a sloping strip of timber, plastic or metal located at the bottom of an exterior door that ensures rainwater runs away from the panel and the bottom edge of the door.

Door frame

The door frame is a collective term that covers the head jamb, the stiles, and the cill.

Escutcheon plate

A metal plate that surrounds the keyhole for a sleek, decorative finish.

Premium Composite Doors in Surrey

Interested in a new composite door or composite door repairs? Try our interactive Composite Door Builder, get a FREE quote, give us a call on 01932 344 415, or get in touch online to find out more.

Related reads:

Can composite doors reduce your energy bill?

What is the difference between composite and uPVC doors?

Our quick explanation for the different types of external doors

One-day installation for beautiful new composite doors

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