A seal strip (60A, 60B, 60C, 60F, 60G, 60H, 60J) with an imperforate width-spanning portion (64) first and second rounded edges (65, 66) and one or more strip-thickening elements (67, 68, 74, 76, 82, 84, 90, 91) between the rounded edges. The strip-thickening elements may have transverse slots (80, 86, 88, 93L, 93R, 72, 78) for increased flexibility of the strip. The strip-thickening elements may also have perforations (92) or gaps (69) to admit coolant and/or to reduce weight. Folded embodiments (60A, 60B) may have dimples (70) on the width-spanning portion (64) to limit bending of the folded portions (67, 68, 74, 76). The seal may be slidably mounted in opposed slots (58A, 58B) in respective adjacent turbine components (54A, 54B), filling a width (W) of the slots, and a side of the seal may be cooled by compressed air (48).