### substance | filling:

Mercury filling
* are illegal in three European countries.
* can induce serious side-effects in individuals overly sensitive to mercury.
* require the removal of the middle third of the tooth.

Fissile material
* are, in general, necessary for building nuclear explosives.
* can sustain nuclear chain reactions.

Flammable material
* Most flammable materials contain substances.
* become readily combustible in molten state

### substance:

Fleece
* comes in a variety of thicknesses
  - many shapes and sizes, and for every climate and activity
* contains inner coat of fine fiber and a protective outer coat.
* does have a light plush face and inner ears.
* has the same insulation as wool at half the weight.
* highly breathable and lightweight fabric.
* is also a popular warmth layer as well as down jackets.
* is often acrylic fleece rather than genuine wool from sheep
  - synonymous with polyester but in fact refers to the treatment of the fabric
  - perfect for curling up under on cold winter days
  - petroleum based polyester
  - relatively light and dries fast
* is superior to wool clothing as it is lighter and dries faster
* is the most well-known fabric for trapping heat
  - wool of a lamb
  - warm, soft to the touch and has great insulative properties
* light woven fabric that provides vital protection from cold.

### substance | fluff:

Fluffy bedding
* is dangerous for hamsters.
+ Hamster
  * Fluffy bedding is dangerous for hamsters. Plain toilet paper is also a cheap, safe option, so is straw. Hamsters eat mostly hamster food sold at a pet shop, but they also eat almost any vegetables and fruits in very tiny portions. Hamsters store food in the sides of their mouths. They need a water bottle with fresh water to drink from, and something to chew on to trim their teeth. Hamster teeth grow constantly.

Fluorescent material
* Most fluorescent materials contain substances
  - toxic substances
* are most effective to daylight conditions.
* show up in daylight and at dusk.

Foreign material
* Some foreign materials create immune imbalances
  - system imbalances
* inoculated into the cornea can present as infiltrates.

Foreign substance
* Any foreign substance entering the water can hurt marine life.
* enter shells.
* tend to be immunogenic.

### substance:

Fur
* Most fur acts as insulation.
* Most fur comes from animals
  - farm animals
  - consists of layers
* Most fur has different length
  - structures
  - protects skin
* Most fur provides protection
  - ranges in color
  - serves as insulation
  - furs handle snow and a light rain with ease
* Some fur comes from animals caught in horrific traps
  - covers ears
* Some fur has different texture
  - fringes
  - salt
* Some fur provides nutrients
  - thermal insulation
* adorn the collars, wrists or just the inner lining of coats or jackets.
* are likely to range from furry and hairy effects to smoothly glowing surfaces.
* come in all colors and descriptions.
* contributes to huge success
* has crucial roles
  - functions
  - important roles
  - quality
  - superior quality
  - unusual structures
* is animal skin
  - warmth

### substance | fur:

Beaver fur
* consists of short fine hairs for warmth and longer hairs for waterproofing.
* has long shiny guard hairs that repel water.
* is fur
  - soft and shiny, and it wears well
* varies from shiny dark brown to yellowish brown.

Dense fur
* Most dense fur provides protection.
* Some dense fur has spots.
* Some dense fur provides insulation
  - thermal insulation
* indicates the depth of cold at the altitudes they inhabit.
* traps a layer of air next to the skin, providing excellent insulation.

Dorsal fur
* Some dorsal fur provides effective insulation
* is long and soft, which contrasts to the short and coarser fur of the venter.

Fake fur
* is far kinder to the environment than real fur.
* make terrific animals.