Is it the same thing as dimethicone?

Same chemistry, different architecture. Dimethicone is a chain; this is those chains cross-linked into a network, which is why it feels powdery rather than slippery.

Does it suffocate skin or clog pores?

The molecule is far too large to enter the stratum corneum, and silicone films pass water vapour rather than sealing skin. Ordinary cleansing removes it.

Does it shrink pores?

No. It fills the surface around them and scatters light so they are less visible, which is an optical effect that ends when the product comes off.

Why does my primer feel like powder?

That dry, velvety slip is the elastomer. It is the main sensory reason the material is used.

Do I need a special cleanser?

Not strictly, but an oil or balm cleanser removes silicone films more comfortably and more completely than a foaming wash.

Dimethicone Crosspolymer — Ingredient Guide

How it works

Linear silicone is a chain. Cross-link those chains to one another and you get a network — an elastomer — which cannot flow like a fluid but can swell, soaking up silicone oil the way a sponge takes water. What reaches the formulator is usually that swollen gel rather than a dry powder, and it is the reason a mattifying primer can feel like almost nothing and still behave like a solid.

On skin the elastomer does three things at once. It has a dry, velvety slip quite unlike an oil, so the whole formula spreads more easily and finishes less greasy. It settles into surface irregularities and scatters light, which lowers the visible contrast of pores and fine lines — the soft-focus or blur effect. And the swollen network takes up some sebum, which is why it appears in products sold on staying matte.

The evidence

The sensory and optical effects are not in dispute; they are the reason the material exists and they are visible within seconds. What deserves saying plainly is what they are: an appearance change produced by something sitting on the surface, lasting exactly as long as it stays there. Nothing here acts on the skin's own structure, and nothing makes a pore smaller.

On the standing accusations against silicones, the chemistry is the same as for linear dimethicone. The molecules are far too large to cross the stratum corneum, silicone films are permeable to water vapour rather than airtight, and ordinary cleansing removes them. An elastomer is if anything less occlusive than the linear polymer, because a swollen network is not a continuous sealed layer.

Suitability

Best suited to oily and combination skin, where the matte finish is the point
Well tolerated in general; reactions to silicones of this kind are uncommon
Often the reason a sunscreen or primer feels dry rather than greasy
Not an active, and nothing in a routine depends on it

Concentration

No figure is quoted, and one would mislead. The raw material is supplied as a dispersion in silicone fluid rather than as a pure substance, so a percentage on a label is not a percentage of elastomer. The level is set by the texture the formulator is after.

Conflicts & combinations

Nothing conflicts with it. Silicone-rich layers and water-based gels applied wet over one another are the classic pilling combination, so the practical rule is to let each layer set. A balm or oil cleanser lifts silicone films more comfortably than a foaming wash does.