Viscous fluid for damper and damper

Provided are: a viscous fluid for dampers, which has high damping force, excellent repeatability, and low temperature dependence; and a damper. Provided is a viscous fluid for a damper, the viscous fluid containing the following (A) and (B): 15-95% by mass (inclusive) of (A) and 5-85% by mass (inclusive) of (B) with respect to 100% by mass of the total polyisobutylene, (A) being a high molecular weight polyisobutylene having a viscosity average molecular weight of 80,000-110,000 (inclusive), and (B) being a high molecular weight polyisobutylene having a viscosity average molecular weight of 9,000-10,000 (inclusive). (B) A low molecular weight polyisobutylene having a number average molecular weight of 10,000 to 20,000 (inclusive). In addition, the present invention provides a damper using the viscous fluid for a damper as a viscous fluid. 提供一种高衰减力且重复性优异、温度依赖性低的减震阻尼器用粘性流体以及减震阻尼器。本发明提供一种减震阻尼器用粘性流体，其中，所述减震阻尼器用粘性流体含有下述的(A)以及(B)，将聚异丁烯整体设为100质量％，所述(A)为15质量％以上且95质量％以下，所述(B)为5质量％以上且85质量％以下，(A)粘均分子量为80,000以上且110,000以下