R-value Refers to the resistance a window has to thermal transfer or heat flow. The higher the value, the better the insulation.
	Rabbet This is a long grain cut along the edge of a piece of wood.
	Radiation Radiation is the transfer of energy by light rays. In winter, Low-E glass reduces the amount of radiant heat loss to the outdoors by reflecting the radiant heat back into the house. In summer, the energy is reflected back outside and prevented from entering the house.
	Radius casings This type of decorative trim is used around the rounded interior perimeter of a window frame.
	Radius lite For divided lites, a radius lite is an available grille pattern.
	Radius straps A radius strap is a decorative metal accent placed where a stile meets the radius top on door.
	Radius window This type of window features curved components. It may include full round, half-round, quarter-round, arch top and springline products. It may be available in fixed or operating configurations.
	Rail The horizontal members on the framework of a sash or panel.
	Rail straps A rail strap is a T-shaped decorative metal accent placed where a stile meets a rail on a door.
	Rain glass This type of glass is completely obscure and features textured, vertical streaks. It may also be referred to as Costwald glass.
	Raised Door Panel A door panel on which the edges have been contoured or shaped to provide an aesthetically appealing, three-dimensional effect.
	Raked top This refers to a door with a top that slopes down and outward from the center.
	RBS casing RBS casing is a proprietary type of moulding profile.
	Recessed sash retainer This hardware component is designed to be invisible to the person operating the window.
	Reed glass This is an English type of glass with a bold, linear pattern.
	Reflective glass Reflective glass is coated to reflect visible light and solar radiation striking the surface of the glass.
	Regrind This is the material that results from the process of breaking down vinyl extrusions for re-extrusion.
	Reinforcement bar Featuring a steel or aluminum profile, this type of bar is used to reinforce vinyl windows and patio doors.
	Relative Humidity The ratio of the amount of water vapor in the air compared to the maximum amount that could be present (usually expressed in a percentage); 100 percent is when the air is totally saturated with moisture.
	Removable full surround lites See full surround wood grilles.
	Removable interior grilles These are grille bars held in place on the interior with grille pines in the stiles and rails.
	Removable Operator Cover A plastic or metal cover which conceals the operating hardware on a casement or awning window.
	Replacement products A term is used to describe replacement windows and doors, these products take the place of an existing window or door. Replacement often may be done with little or no disruption of the existing opening. They are also known as retrofit products.
	Resin This commonly used industry term refers to the raw materials used by PVC extruders to produce vinyl window profiles. The work is also used to describe a liquid material that is used in the production of laminated glass.
	Retro This general term used to describe replacing an existing opening (i.e., to retrofit).
	Retrofit products See replacement products.
	Reveal The space between the window sash or door panel and the frame.
	Ripple glass This type of glass features a pronounced rippled texture.
	Riser The structural component fixed to the bottom of the stationary sash in a horizontal sliding window.
	Roll-form cladding Cladding that is not extruded aluminum. Roll-form cladding is cut from a larger sheet of aluminum and is formed through a series of rollers. It is non-extruded.
	Roller A roller is the round wheel used in a sliding window or patio door on which the operating sash or panel travels. For this reason, a sliding window may also be called a roller window.
	Roof window This is an operable unit similar to a skylight placed in the sloping surface of a roof.
	Roto-Operator A window-opening mechanism that has a handle that turns in a circular pattern; used on awning windows.
	Rough Opening The framed opening in a wall where a window or door is to be installed.
	Round handle Used for casement and awning windows, a round handle has a circular knob to operate the window. See also crank handle.
	Round top This is a feature on a window or door with a 180-degree curve at its top. It is also called a true radius top.
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