Each point of Damage Resistance (DR) removes one point of damage in a narrow domain (e.g., heat, radiation, crushing, projectiles). Characters with DR take no damage under conditions that normally cause harm. DR can be selected many times.
Some attacks remove damage resistance. Each point of damage resistence is treated as two stress slots against this kind of drain. For example, TALOS armour has DR3 vs Environmental Hazards. CDWs have a +6 attack against environmental protections like that, and tend to attack in overwhelming swarms so defenders run out of reactions. The first unopposed attack can be soaked (12345xDR+3). An ally aids the target (+1 defence) against the second attack, so it can be soaked too - but with two slots filled, the DR is reduced to +2 (1234xxDR+2). One more CDW attacks. With no more allies or reactions, that one lands, making the SCHEP layer useless. Note that no stress or other damage is done to the person wearing the armour.
Normal HazMat suits have DR3 vs Environmental Hazards, but that DR is vulnerable to piercing and cutting. Someone wearing such a suit has to be very careful to avoid sharp objects, as they are effectively attacks against the suit's DR.